Naphthalene burns with a yellow sooty flame. This is because

While burning hydrocarbon fuels, if we see a yellow flame with lots of black smoke, it means that the fuel is :

Which one of the following is a covalent compound?

Which one of the following acids is secreted by leaves of Nettle that causes painful stings?

Which one of the following oxides is a neutral oxide?

Which one of the following allotropes of carbon is isomorphous with crystalline silicon?