C. The temperature decreases because the most energetic molecules escape.
The number of neutrons in an atom is the number of particles present in its nucleus.
The atomic number is the number of protons whereas the mass number is the number of protons and number of neutrons together
This implies that the number of neutrons is the atom's mass number
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%Mass
Ar C = 12 g/mol, Mr C₄H₁₀ = 58 g/mol, Ar H = 1 g/mol

or
