A) Magnesium + Chlorine -> Magnesium chloride ( Mg + Cl2 -> MgCl2)
b) Potassium + Oxygen -> Potassium oxide
( 2K + O2 -> K2O )
c) Sodium + Bromine -> Sodium bromide
( 2Na + Br2 -> 2NaBr)
d) Carbon + Oxygen -> Carbon dioxide
( C + O2 -> CO2 ) This reaction occurs when heated.
Explanation
Radius of neon atom : 69 pm = 
Volume occupied by the one atom:

given that
atoms are present in 1L
1 L = 0.001 
The volume occupied by the
neon atoms

Fraction of volume occupied by the neon atom:


The fraction of of volume occupied by the neon atom is very less than the 1 L which indicates the presence of large amount of empty space between the atoms of the gas.
Answer: Uranium enrichment. Uranium is used to fuel nuclear reactors; however, uranium must be enriched before it can be used as fuel. Enriching uranium increases the amount of uranium-235 (U235) that can sustain the nuclear reaction needed to release energy and produce electricity at a nuclear power plant.
Explanation:
Entropy of a reaction ΔS∘rxn is the degree of disoderliness in a system. Gases generally have a higher degree of disorder compared to liquids. Hence for the reaction 2H2(g)+O2(g) ⟶ 2H2O(l), the entropy decreases sice the reactants are in the gaseous state and the products is in the liquid state of matter