Among the following, covalent compound is                             

The nature of bond in a molecule is decided by the difference in the electronegativity of bonded atoms. If electronegativity difference is less than 1.7 it is a covalent bond, where as if it is greater than 1.7 it is ionic bond. In methane molecule between carbon and hydrogen very little electronegativity difference is there(less than 1.7), hence it is a covelent molecule.