1 nano is equal to 10^-9 m

Its true, that mica is a good conductor of heat but a bad conductor of electricity, mica heats the iron's base but not give electric shock. That's why it is use in electric iron.

The energy used in rolling the fuel tank on the coal tar is much less because in pulling the fuel tank via an inclined plane the frictional force to be overcome will be greater than rolling it down the plane.

One is obviously out. Two is out because if two unequal forces n and p act on an object the resultant with the minimum force in magnitude is |n - p|, which will never be 0 if n =/= p. Three can be easily resolved with a quick example. Imagine an object with three concurrent forces acting on it. Two forces, n = 3 N and p = 4 N, create an angle with eachother such that the resultant is 5 N. 180 degrees from the resultant, a force, r = 5 N, is acting on the object. Thus three unequal vectors on an object can result in 0.