Smog', which means 'smoke' plus 'fog', irritates eyes and the throat. Smog is mainly caused by pollutants from automobiles and industries when they:A.Hit a dense shower of snow flakesB.React photochemically, due to the effect of ultraviolet lightC.Form a smoke ringD.React with oxygen in the air due to lightning electrical discharge from clouds

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)