[yangyangg]

But you said other options are strong acids??

[AWK]

You stll have two options: c and d

[yangyangg]

Why pH would not change when strong acids are added?

[AWK]

It depends on volumes and concentrations of both solutions

[Albert]

When I came back from the University I constantly thought about this question and I realized I had completely missed the whole point.
That's what you get doing things while you're tired and in a hurry.

 

Luckily, you can always rely on the Poles. 

[bodegas]

I'm thinking that this is one of those high school questions that has no correct answer...
the dissolution of an acid would change the pH but wouldn't it be just marginally (because of the logarithmic scale of the pH)? Wouldn't any other strong acid in the conditions presented change the pH of the solution, even if marginally also? HNO3 donates one proton to solution but its pKa is different from that of hydrochloric acid. Wouldn't you say that the only true answer would be to add 50 mL of hydrochloric acid at C=1,0 M?

[Borek]

I'm thinking that this is one of those high school questions that has no correct answer...

Exactly, I just refrained myself from commenting on the lack of correct answer as at the time I have posted much simpler mistakes were in action Getting into such details if the OP is in HS doesn't make much sense BEFORE expected answer is found

[AWK]

Question suggests answer with two significant digits!

[mike]

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?

[Borek]

Am I right?

That's probably expected reasoning, although nitric acid is the weakest of the strong so in concentrated solutions (like 1M) its pH is lower than that of HCl.

However, with AWK remark about significant digits C IS the correct answer, as the pH change will be in the several hundreths range.