Solution

Option $$(A),\ (C)$$ and $$(D)$$ are correct. $$(A)$$: A pi bond is weaker than sigma bond.A sigma bond is the end-to-end overlap of the bonding orbitals.whereas, a pi bond is the side-to-side overlap of (usually) two p-orbitals. This places the electron density above and below the plane of the nuclei with a node in the middle. The nodal region reduces the degree to which the orbitals overlap and therefore a pi bond is less strong than a sigma bond between the same two elements. $$(B)$$: A sigma bond is stronger than $$\pi$$ bond. $$(C)$$: A(=) bond is stronger than a single bond. It is because there are more electrons to be shared by the two atoms, so the nuclei are more attracted. The bonds to be longer because there are more electrons and the electrons would repel each other more. $$(D)$$: A covalent bond is stronger than $$H$$-bond. The difference in strength is due to the fact that hydrogen bonding is an intermolecular force due to dipole formation in molecules. Covalent bonding is due to the sharing of valence electrons between atoms (intramolecular attraction).