Answer: The gravitational acceleration on planet X is 5 N/kg
On Earth (with the gravitational accelartion g_E) the mass of 2kg will correspond to

On planet X we are told the same measure is only 10N. Since there is a proportional relationship between g and F, we can calculate g_X:

This applies to nuclear reactions, specifically nuclear fission.
This huge release of energy has been used in atomic bombs and in the nuclear reactors that generate electricity.
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A gerund usually ends wit -ing, so we must find the word that includes that.
Loading includes ing at the end.
Final answer: b. loading