A molecule is a group of two or more atoms of the same element, joined by covalent bonds. The simplest molecules have to atoms like some gaseous elements such as nitrogen (N2), while a compound is a pure substance constituted by atoms of different elements joined through chemical bonds in defined proportions and that can only be decomposed into the elements of origin by chemical reactions.
In chemistry, all compounds are molecules but not all molecules are compounds. A molecule is the joining together or combination of two atoms of an element e.g when two Nitrogen (N) atoms come together to form N2 molecule. A compound, on the other hand, is a molecule that consists of atoms of different elements e.g atoms of Hydrogen and Oxygen combining to form water (H2O) compound.
Having defined both terms, the difference between a molecule and a compound is that for a molecule to be considered a compound, it must contain atoms of different elements. Based on this, all the options in the question are molecules but (N2) molecule has only atoms of the same element (Nitrogen). Hence, N2 cannot be considered a compound.
