Density increases with the temperature, true.
D) burning magnesium ribbon, as combustion is a chemical reaction so causes chemical change. The other 3 options do not involve reactions so there isn't a chemical change.
Mole ratio for the reaction is 1:1
no of moles in NaOH that reacted= 1*21.17/1000=0.02117mols
molarity of HCl=0.02117*10/1000
=2.117M
