Simon and Nirav are carrying out an investigation to find which of the metals X and Y produces the higher temperature in a reaction with hydrochloric acid. Simon measures out 10cm cube of hydrochloric acid in a test tube. He measures the temperature and then places a small piece of metal X into the acid. He sees bubbles of gas given off. When the reaction finishes, he measures the temperature again Nirav measures out 10 cube of hydrochloric acid in a test tube. He measures the temperature and then places a piece of metal Y into the acid. He also sees bubbles of gas given off. When the reaction finishes, he measures the temperature again. Question 1=Which variable did Simon and Nirav need to change in their experiment?