When hydrogen sulphide gas is passed through a blue solution of copper sulphate, the color of the solution fades and a black precipitate is obtained.a) Name the type of reaction mentioned above.b) Why does the color of the solution fade away?c) Write the chemical name of black precipitate formed.d) Give the balanced chemical equation for the reaction involved.

Which of the following is likely to be least stable?

• (A) Ca₄₀
• (B) Mn₅₅
• (C) Sn₁₁₉
• (D) Al₃₀

Which of the following is not a Lewis acid?

• A. BF₃
• B. AlCl₃
• C. FeCl₃
• D. PH₃

Which of the following is not a property of compounds?

• (A) They are made up of two or more kinds of atoms.
• (B) They cannot be broken down into two or more simpler substances by physical means but by chemical means only.
• (C) Properties of compounds differ from those of their elements.
• (D) None of the above.

Which of the following is polar?

• A. NF₃
• B. BF₃
• C. SF₄
• D. SiF₄

Which of the following metals exists in their native state in nature?

• (i) Ca
• (ii) Au
• (iii) Zn
• (iv) Ag

A. (i) and (ii)

B. (ii) and (iii)

C. (ii) and (iv)

D. (iii) and (iv)