Questions

Uranium is not a fossil fuel whereas coal, petroleum and natural gas are all natural resources.

Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals. In common dialogue, the term fossil fuel also includes hydrocarbon-containing natural resources that are not derived from animal or plant sources

A metalloid is an element with properties between metals and non metals or the mix of both.

The six metalloids are arsenic, silicon, germanium, boron, antimony and tellurium.

Hence, silicon is the only metalloid in the given list.

( int t ; t = a, a = b, b = t ;);

This code won't compile since declaration of t cannot occur within parentheses.

Stamps are what travel around the worldstaying in one spot. Slippers and walking stick can also travel around the world but they will not stay at one spot. So they are eliminated.