Of three persons, two take relish, two take pepper, and two take salt. The one who takes no salt takes no pepper, and the one who takes no pepper takes no relish. Which of the following statements must be true?
Let the three people be A, B, and C
S = Takes salt
S = No salt
P = Takes Pepper
P = No Pepper
R = takes relish
R = No relish
The question says "The one who takes no salt takes no pepper, and the one who takes no pepper takes no relish."
So, assume C does not take salt and consequently does not take pepper.
So, C = S and P
Because S = P
The question also says that
P = R
So, S = P = R
Essentially, C = S + P + R that is C doesn't take any of the three things.
So, A = P+S+R
B = P+S+R
That is A and B take all the three items.
I. The person who takes no salt also takes no relish.
Yes, true. C doesn't take relish.
II. Any of the three persons who takes pepper also takes relish and salt.
Yes, true. A and B take all of the three.
III. The person who takes no relish is not one of those who takes salt.
Yes, true. C does not take salt.
If you understand that
A = P+S+R
B = P+S+R
C = P+S+R
Only then will you be able to answer the question correctly.