d
If the distance between two objects is doubled the gravitational force becomes one fourth since,

\(F = G \frac{ m _1 \times m _2}{ R ^2}\)

Where \(R\) is the diatnce between the bodies .

So, if \(R^{\prime}=2 R\), then

\(F^{\prime}=G \frac{m_1 \times m_2}{R^2}\)

\(F ^{\prime}= G \frac{ m _1 \times m _2}{4 \times R ^2}=\frac{ F }{4}\)