Answer :
(a) it was formed when electrons were shared
NaCl is an ionic bond which means an electron(s) was transferred (from one atom to another to make them stable) not a covalent bond which means an electron(s) was shared
NaCl is an ionic bond which means an electron(s) was transferred (from one atom to another to make them stable) not a covalent bond which means an electron(s) was shared