JEE Main 2020 · 9 January · morning · Single correct · +4 / −1
'X' melts at low temperature and is a bad conductor of electricity in both liquid and solid state. X is :
- (a) Mercury
- (b) Carbon tetrachloride
- (c) Zinc sulphide
- (d) Silicon carbide
Answer and solution
Answer (b) Carbon tetrachloride
Solution
Chemistry ma’am · 3 steps
Low melting point and no conduction even when molten: that is the signature of a molecular solid.
- Low melting point. A low melting point means only weak forces hold the particles together. That points to a molecular solid, where whole molecules are held by weak intermolecular forces.
- Bad conductor. To conduct, a substance needs free electrons, as in metals, or mobile ions, as in a molten ionic solid. A non-polar molecular substance has neither, so it does not conduct as a solid or as a liquid.
Substance Type of solid Melting point Conducts? Mercury metallic low yes, free electrons in both states CCl₄ molecular (non-polar) low no, in either state ZnS ionic high no as a solid, yes when molten SiC covalent network very high poor - So. Only carbon tetrachloride passes both tests, so X is CCl₄, option (b).
The idea to keep. Match properties to the type of solid: molecular means low melting point and insulator, ionic means high melting point and conducts only when molten, metallic always conducts.
Answer from the NTA final answer key. Solution by PrepWiser.