Answer:
A.The attraction between the shared electron and the protons in each nucleus
Step-by-step explanation:
Covalent bonds are formed when the atoms involved in bonding share their electron pairs.
When the atoms comes close to each other two types of forces acts on it:
1)Repulsive forces: electron-electron repulsion and nuclei-nuclei repulsion
(Similar charges repel each other,electrons are negatively charged and protons are positively charged)
2)Attractive forces: nuclei-electron attraction or
The attraction between the shared electron and the protons in each nucleus
A covalent bond is formed when the net force of attraction balances the net force of repulsion and the system acquire minimum energy.