Free Reactions of Group IV Elements MCQs with Answers

1. The elements of group IV show a gradation in character from

• A. metallic carbon to non metallic lead
• B. non metallic carbon through metalloid silicon and germanium to metallic tin and lead
• C. entirely metallic throughout
• D. entirely non metallic throughout

Explanation: Carbon is a non metal, silicon and germanium are metalloids used as semiconductors, and tin and lead are true metals, so group IV shows the clearest metallic gradation of any group. The reason is that ionisation energy falls down the group as the atoms get larger. This trend of increasing metallic character down a group applies across the p block.

2. In group IV, the stability of the plus 2 oxidation state relative to the plus 4 state

• A. decreases down the group
• B. is the same throughout
• C. is zero for all members
• D. increases down the group, so lead two compounds are more stable than lead four

Explanation: This is the inert pair effect: the two s electrons of the outer shell become progressively harder to involve in bonding as the group is descended, so tin favours plus 4 while lead favours plus 2. It follows that lead four compounds such as PbO2 are strong oxidising agents, readily reverting to lead two. The same effect appears in groups III and V.

3. Carbon differs markedly from the other members of group IV mainly because it

• A. is small, has no available d orbitals and forms strong multiple bonds with itself
• B. has a much larger atomic radius
• C. is a metal
• D. has a full outer shell

Explanation: Its small size lets carbon form stable double and triple bonds and catenate into long chains, which is the basis of the whole of organic chemistry, while the absence of d orbitals limits it to a maximum covalency of four. Silicon and the heavier members can expand their octets using d orbitals, so silicon forms SiF6 2- while carbon cannot form the analogous ion. Carbon has four outer electrons, not a full shell.