Chem question

The answer is: (A) The boron atom in BCl3 has six electrons in its outermost shell, whereas the phosphorus atom in PH3 has eight.

(A) is correct.
In BCl3, there are 3 B-Cl bonds and no lone pair of electrons, and thus the B atom has 6 electrons in its outermost shell.
In PH3, there are 3 P-H bonds and 1 lone pair of electrons, and thus the B atom has 8 electrons in its outermost shell.