The number of electrons in the valence shell of elements A and B, are 6 and 7 respectively. What is the formula and type of bonding in a compound formed by these elements?

A.     ${{\text{A}}_{\text{2}}}{\text{B}}$, covalent

B.     ${\text{A}}{{\text{B}}_{\text{2}}}$, covalent

C.     ${{\text{A}}_{\text{2}}}{\text{B}}$, ionic

D.     ${\text{A}}{{\text{B}}_{\text{2}}}$, ionic

B