For this multiple question:
The correct answer is B. However, I don't understand.
You are halving the volume so for the original solution the number of moles of HCl is 0.1 moles and in the new solution, the number of moles of HCl is 0.05 if we are using the same concentration.
Therefore as there are less number of moles, won't the temperature increase (ie. energy release) get halved?