'X' melts at low temperature and is a bad conductor of electricity in both liquid and solid state. X is:

Strategy: Identify the substance that melts at low temperature and is a bad conductor of electricity in both solid and liquid states.

Step 1: Analysing the Properties

• "Melts at low temperature" → Low melting point → likely a molecular compound (not ionic or covalent network).
• "Bad conductor in solid AND liquid" → eliminates metals and ionic compounds (ionic compounds conduct in liquid state). This points to a non-ionic, non-metallic substance.

Step 2: Evaluating Options

• Zinc sulphide ($\ce{ZnS}$): Ionic, conducts electricity in liquid state. ❌
• Mercury ($\ce{Hg}$): Metal, good conductor in liquid state. ❌
• Silicon carbide ($\ce{SiC}$): Covalent network solid, extremely high melting point (~2730 °C). ❌
• Carbon tetrachloride ($\ce{CCl4}$): Covalent molecular compound, low melting point (−23 °C), bad conductor in both solid and liquid states (no ions or free electrons). ✅

$\boxed{\text{Answer: (D) Carbon tetrachloride (}\ce{CCl4}\text{)}}$