A-Q,
B-P,
C-P,
D-Q
(A) in terms of density g = (4/3)πρ GR i.e. g ∝ ρR
given : ρ1 = 2ρ
R1 = (R/2)
hence (g / g') = (ρR / ρ1R1)
∴ (g / g') = [ρR / {2ρ × (R/2)}] = 1
g = g'
i.e. acceleration due to gravity remains same
(B) Gravitational Potential ∝ distance
hence if planet is having half radius, then gravitational potential on the surface will also be half.
(C) Similarly gravitational potential at centre will be half of that for earth centre.
(D) Gravitational field strength remains unchanged.