Potential at center = Potential due to mass 1 + Potential due to mass 2
$R_1-R_2=0.5\;m$
$R_1=R_2=0.5$
$\qquad= \large\frac{-Gm_1}{r_1}-\frac{Gm_2}{r_2}$
$\qquad= -6.67 \times 10 ^{-11} \bigg[ \large\frac{10^2}{5}+\frac{10^3}{5}\bigg]$
$\qquad= 1.47 \times 10^{-7} J/kg$
Hence d is the correct answer