Answer:
The acceleration due to gravity of that planet is, gₐ = 1.25 m/s²
Step-by-step explanation:
Given that,
Mass of the planet, m = 1/2M
Radius of the planet, r = 2R
Where M and R is the mass and radius of the Earth respectively.
The acceleration due to gravity of Earth, g = 10 m/s²
The acceleration due to gravity of Earth is given by the relation,
 g = GM/R²
 Similarly, the acceleration due to gravity of that planet is 
 gₐ = Gm/r²
where G is the Universal gravitational constant
On substituting the values in the above equation
 gₐ = G (1/2 M)/4 R²
 = GM/8R²
 = 1/8 ( 10 m/s²)
 = 1.25 m/s²
Hence, the acceleration due to gravity of that planet is, gₐ = 1.25 m/s²