If a body weighs 12N on the surface of the earth, how much will it weigh on the surface of the moon where acceleration due to gravity is only one-sixth of that on earth's surface?

Weight is mass x g. Since mass is constant and g is only  $\frac{1}{6}th$of that on the earth. The weight on the moon is only  $\frac{1}{6}th$ of that on the earth. 

Therefore 2N i.e (b) is the answer.