Answer
See the answer below.
Work Step by Step
a) Since B and Ga are in group 13 and atomic radius increases down a group, the BCl bond is shorter than the GaCl one.
b) Since C and Sn are in group 14 and atomic radius increases down a group, the CO bond is shorter than the SnO one.
c) Since S and O are in group 16 and atomic radius increases down a group, the PO bond is shorter than the PS one.
d) Since O and N are in period 2 and atomic radius decreases along a period, the CO bond is shorter than the CN one.
