Covalent bonds are formed when valence electrons are between a. shared; ions b. shared; atoms c. transferred; ions d. transferred; atoms

Option B is correct.

B.shared; atoms

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding.

B. shared; atoms

Explanation:

Covalent bond is formed by sharing of electrons between two atoms. In this way full outer shell is achieved by both the atoms. Since there is no gain or loss of electrons, no ions are formed in the process.

It is usually formed between the atoms of similar electronegativity. It can be of many types like sigma bond, pi bond etc. If a pair of electrons is shared, it's a single bond. If two pairs are shared, it's a double bond and if three pairs are shared, it's a triple bond.

geographic isolation