According to question,
We can draw a figure , in which Subbu is to the left of Pappu, Revathi is between Subbu and Nisha, Aruna is between Pappu and Keerthana.
As shown in figure , Subbu is to the left of Pappu.
Sitting sequence :-

Draw a figure on the basis of above given question ,
the father was found to be sitting to the left of the son and right to the grandfather. Mother was sitting to the right of her daughter but left to the grandfather.
As shown in figure , Grandfather is occupying the central place .
Sitting arrangement :-

Draw a figure on the basis of above given question ,
S is between T and Q and Q is to the immediate left of R. P is to the immediate left of T.
As shown in figure , S is in the middle.
Sitting arrangement :-

Draw a figure on the basis of above given question ,
Y is at the left of X, W is sitting at the right of Z. V is sitting at the right of X and W is sitting at the left of Y. If Z is sitting at one end of the row .
From figure , It shows that Y is in the middle.
Sitting arrangement :-

According to question,
We can draw a figure , in which A and B are sitting face to face. D is not sitting next to A but can see the facial expression of A clearly. B is talking to C who is sitting opposite to him.
From given figure it is clear that , A and C are sitting together.
Sitting arrangement :-

According to question,we have
Rashi's position = 15th from the left
Ramesh's position = 29th from the right
After interchanging their positions ,
Rashi's position = 26th from left
? Total number of students = Rashi's position + Ramesh's position - 1
Total number of children in the row = 26 + 29 ? 1 = 54
As shown in figure -

According to question,
We can draw a figure , in which A is on the right of B, E is on the left of B, but to the right of C. If A is on the left of D .
From given figure it is clear that , B is in the middle.
Sitting arrangement :-

According to question,
If P is sitting second to the left of S and Q is sitting third to the right of R. T sits immediate right of S, Q is not on immediate right or left of S.
It is clear that , S is sitting to the immediate right of R.
Sitting arrangement :-

Draw a figure on the basis of above given question ,
E is standing 40 metres left to B. A is standing 20 metres left to C. D is standing 20 metres right to E and 50 metres right to C.
Therefore , S is sitting to the immediate right of R.
sitting sequence :-

According to question,
We can draw a figure , in which G is between A and E .F and A have one boy between them . E and C have two boys between them . D is to the immediate .C and B have three boys between them.
From given figure it is clear that , E is second from left.
Sitting arrangement :-