Có 4 lọ dung dịch không nhãn: NH₄Cl, (NH₄)₂SO₄, Na₂SO₄, NaOH. Thuốc thử nào sau đây có thể nhận biết các chất trên?

để đánh giá độ nhiễm bẩn không khí của một nhà máy, người ta tiến hành như sau: lấy 2 lít không khí rồi dẫn qua dung dịch Pb(NO₃)₂ dư thì thu được chất kết tủa màu đen. Hãy cho biết hiện tượng đó chứng tỏ trong không khí có chứa khí nào trong các khí sau?

Có 4 lọ dung dịch không nhãn: NH₄Cl, (NH₄)₂SO₄, Na₂SO₄, NaOH. Thuốc thử nào sau đây có thể nhận biết các chất trên?

Để xác định hàm lượng FeCO₃ trong quặng xiđerit ,người ta làm như sau : Cân 0,600 gam mẫu quặng ,chế hóa nó theo một quy trình hợp lí ,thu được dung dịch FeSO₄ trong môi trường H₂SO₄ loãng .Chuẩn độ dung dịch thu được bằng dung dịch chuẩn KMnO₄ 0,025M thì dùng vừa hết 25,2 ml dung dịch chuẩn .Thành phần phần trăm theo khối lượng của FeCO₃ trong quặng là :

Có 6 dung dịch riêng rẽ, mỗi dung dịch chứa 1 cation sau đây: , Mg²⁺_' Fe²⁺_' Fe³⁺, Al³⁺, Ba²⁺ (nồng độ khoảng 0,1M). Chỉ dùng một thuốc thử để nhận biết các dung dịch trên là:

Trường hợp nào sau đây được coi là không khí sạch ?

có 3 dung dịch hỗn hợp X ( NaHCO₃ và Na₂CO₃); Y ( NaHCO₃ và Na₂SO₄) và Z ( Na₂CO₃ và Na₂SO₄). Để nhận biết được 3 dung dịch trên cần dùng 2 dung dịch là;

để phân biệt các dung dịch CaCl₂, ZnCl₂, MgCl₂ và AlCl₃ ở trong các lọ riêng biệt có thể dùng:

Có 4 mẫu kim loại là Na, Ca, Al, Fe. Chỉ dùng thêm nước làm thuốc thử thì nhận biết được tối đa

Giả sử chuẩn độ dung dịch CH₃COOH 0,1M bằng dung dịch chuẩn NaOH 0,1M. Biết pH của dung dịch CH₃COOONa 0,05M bằng 8,74. Sự chuẩn độ trên dùng chất nào trong 3 chất chỉ thị metyl da cam, metyl đỏ, phenolphtalein để nhận ra điểm tương đương thì thu được kết quả chính xác nhất?

có thể dùng chất nào dưới đây để phân biệt các dung dịch BaCl₂, Na₂SO₄, MgSO₄, ZnCl₂, KNO₃ và KHCO₃:

Question 24: The author mentions Vivaldi and Tartini in passage as examples of composers whose music___________.    

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.

Công thức tính số tổ hợp là:

Question 23: The word “they” in the passage refers to___________.         

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.

Công thức tính số tổ hợp chập của phần tử là:

Question 26: According to the passage, early violins were different from modern violins in that early violins____________. 

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.

Hệ số của số hạng chứa trong khai triển (với ) bằng:  

Trong khai triển , hệ số của số hạng chứa là:

Question 25: According to the passage, which of the following contributes to a dull sound being produced by a violin?             

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.

Tìm hệ số của trong khai triển .                 

Question 28: The word “strain” is closest meaning to___________.         

Of all modern instruments, the violin is apparently one of the simplest. It consist in essence of a hollow, varnished wooden sound box, or resonator, and a long neck covered with a fingerboard, along which four strings are stretched at high tension. The beauty of design, shape, and decoration is no accident, the proportions of the instrument are determined entirely by acoustical considerations. Its simplicity of appearance is deceptive. About 70 parts are involved in the construction of a violin. Its tone and its outstanding range of expressiveness make it an ideal solo instrument. No less important, however, is its role as an orchestral and chamber instrument. In combination with the larger and deeper-sounding members of the same family, the violins form the nucleus of the modem symphony orchestra. The violin has been in existence since about 1550. Its importance as an instrument in its own right dates from the early 1600’s, when it first became standard in Italian opera orchestras. Its stature as an orchestral instrument was raised further when in 1626 Louis XIII of France established at his court the orchestra known as Les vinq-quatre violons du Roy (The King's 24 Violins), which was to become widely famous later in the century. In its early history, the violin had a dull and rather quiet tone resulting from the fact that the strings were thick and were attached to the body of the instrument very loosely. During the eighteenth and nineteenth century exciting technical changes were inspired by such composer-violinists as Vivaldi and Tartini. Their instrumental compositions demanded a fuller, clearer, and more brilliant tone that was produced by using thinner strings and a far higher string tension. Small changes had to be made to the violin's internal structure and to the fingerboard so that they could withstand the extra strain. Accordingly, a higher standard of performance was achieved, in terms of both facility and interpretation. Left-hand technique was considerably elaborated, and new fingering patterns on the fingerboard were developed for very high notes.