Boron cannot expand its covalency beyond three due to _____.

Boron cannot expand its covalency beyond four due to _____.

Carbon can not expand its valency beyond 4, because

(A) NCl_(3) is known, but not NCl_(5) (R ) Nitrogen can not expand its valency beyond four.

Assertion : The covalence of nitrogen in N_2O_5 is 5. Reason : Nitrogen can expand its covalence beyond 4.

Assertion : The covalence of nitrogen in N_(2)O_(5) is 5 Reason : Nitrogen can expand its covalence beyond 4.

(A) : Nitrogen cannot form pentahalides (R) : Nitrogen cannot expand its octet configuration, due to absense of empty d-orbitals.