Interpret the distance carefully

The body is placed at a distance $2R$ from the surface of the Earth.

So its distance from the center of the Earth is: $r = R + 2R = 3R$

Use variation of gravitational force with distance

Gravitational force on a mass $m$ at distance $r$ from Earth’s center is: $F = \frac{GMm}{r^2}$

On the surface of Earth: $mg = \frac{GMm}{R^2}$

Therefore, at distance $r = 3R$: $F = mg\left(\frac{R}{3R}\right)^2 = mg\cdot \frac{1}{9}$

Substitute values

Given: $m = 90\,\text{kg}, \quad g = 10\,\text{m s}^{-2}$

So on the surface: $mg = 90 \times 10 = 900\,\text{N}$

Hence, $F = \frac{900}{9} = 100\,\text{N}$

Check options

• A: $300\,\text{N}$
• B: $225\,\text{N}$
• C: $100\,\text{N}$
• D: $120\,\text{N}$

The correct option is: $\boxed{\text{C: }100\,\text{N}}$