You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Two forms of boron are naturally occurring, boron-10 and boron-11. What difference exists between a boron atom with a 10 atomic mass units (amu) and a boron atom with 11 atomic mass units (amu)?  
 (A) amount of neutrons (B) number of electrons (C) size of protons and neutrons (D) size of electrons and electron cloud
A

Water freezing is an example of a  
 (A) liquid changing to a solid (B) solid changing to a liquid (C) gas changing to a solid (D) gas changing to a liquid
A

Which of the following properties of ethanol is a chemical property?  
 (A) colorless (B) flammable (C) boils at 78°C (D) density of 0.79 g/cm^3

B