Plz,explain the answer of ques no 20,21 & 24 given in above image.

Dear student
pH=2 thus H+ = 10^-2
pH=4 thus H+ = 10^-4
pH of resulting solution when two acids are mixed in it are :-
N1V1 + N2V2 = NfVf
10^-2 * 1 + 10^-4 * z = 10^2.75 *(1+z) = 0.00177 (1+z)
0.01 + 0.0001 z = 0.00177 (1 +z)
On solving we get,
z= 4.92 which is approximately 5

Kindly post each question separately.

Approved