Conscience and conscious

Conscience means moral sense, ethical feelings or one’s sense of right and wrong.

• His conscience wouldn’t let him steal.

Note that conscience is spelled with science at the end.

Conscience is a noun; conscious is an adjective. It is an inward alertness or awareness.

• Is she conscious yet?
• Were you conscious of his hostility? (= Were you aware of his hostility?)
• He was not conscious when they took him to hospital.

Consciousness is the noun form of conscious.

• The accident victim never lost his consciousness. 

Conscientious is the adjective form of conscience.

A conscientious worker arrives on time and does his duty with utmost sincerity.