Explain why, a salt which does not conduct electricity in the solid state becomes a good conductor in molten state.

In the solid ion compounds, ions are held together by a strong electrostatic forces therefore free moving of ions are restricted. When it dissolves in water or melts it, the crystal structure will break and ions will move freely and conducts electricity. So an aqueous solution of ionic compound conducts electricity and there are plenty of free ions which are able to conduct electric current.