Question

molten sodium chloride or passing current decomposes into sodium metal and chlorine gas. balance it

Answer 1

2NaCl----------2Na+Cl2(g)

Answer 2

Molten sodium chloride decomposes on passing electricity to give sodium and chorine gas. This process is known as Electrolysis as decomposition occurs in presence of electricity. 
Following is the balanced equation for electrolysis. 
2NaCl −→−−−−−−   Electricity    2Na + Cl2