Given below are the atomic numbers of some group 14 elements. The atomic number of the element with lowest melting point is :

Solution

Chemistry ma’am · 4 steps

Melting point falls down group 14, but it bottoms out at tin, not lead. Pb climbs back up a little.

1. Name the elements. Atomic numbers 6, 14, 50 and 82 are carbon, silicon, tin and lead.
2. Why it falls. Carbon and silicon are giant covalent networks. Melting them means breaking strong covalent bonds, so their melting points are very high. Further down, the elements become metals, and their bonding is weaker.

   Z	Element	Bonding in solid	Melting point
   6	C	covalent network	4373 K
   14	Si	covalent network	1693 K
   50	Sn	metallic	505 K, lowest
   82	Pb	metallic	600 K

3. The irregular end. The fall does not continue all the way down. Lead, at 600 K, melts higher than tin, at 505 K. So tin, not lead, has the lowest melting point in the group.
4. So. The element with the lowest melting point is tin, atomic number 50, option (b).

The idea to keep. In group 14, melting point drops from C to Sn as covalent networks give way to metals. Then it rises slightly at Pb. Remember the order C > Si > Ge > Pb > Sn.

Answer from the NTA final answer key. Solution by PrepWiser.