Which of the following is the combination by which Molecular compounds are formed ?

Molecular compounds are usually formed by the combination of two different non-metal.
This is because they share their electrons to complete their octet. Non-metals cannot form ions like metals as they cannot gain or lose as it is not energetically favorable.

So, they go for the sharing of electrons. Non-metals share their electrons through covalent bonds. On the other hand, metals form ions by losing or gaining electrons.