Answer:
Sodium- will loose electron
Silicon - could loose or gain electrons
Oxygen - wil gain electron
Argon - does not gain or loose electron
Explanations
Sodium is a group 1 elements. All group 1 elements have 1 valence electron in their outermost shell which they can easily loose to other atoms to form a stable octet configurations. Hence Sodium will loose electron.
For silicon, it forms a covalent bond with other non metals. Therefore it could loose or gain electrons.
Oxygen is known as one of the electronegative element with 6 valence electrons in its outer shell. This shows that oxygen will need 2 electrons to form a stable octet configuration. Therefore, Oxygen will gain electrons.
Elements that can neither loose nor gain electrons are known to be inert in nature since their outer shell is already complete. Since Argon is inert due to astable configuration, hence it does not gain or lose electrons