This is the simple solution:
A. 50mL of 1.0M sodium chloride solution
False: This would dilute the acid by half so the pH would change.
B. 50mL of 1.0M ethanoic acid
False: weak acid so would change pH
C. 50mL of 1.0M nitric acid
True: pH for 50mL of 1.0M acid will be the same as solution of 100mL of 1.0M acid as concentration is the same.
D. 50mL of 1.0M sulphuric acid
False: Sulphuric acid is diprotic so would make the solution more acidic
Am I right?