Answer:
D. Number of electrons
Chlorine would become a liquid. Its boiling point is around -34 Celsius so at any temperature below that it would be liquid.
I believe the correct answer is D. Because object A on the pH scale reads pH=3. Which means it is more acidic in nature and thus possess a greater hydrogen or hydronium ion concentration than object B, which has a higher value on the pH scale. Object B would thus have a lower hydronium ion concentration than Object A.