ANS:A -

Correction due to sag (same in levels).
C = w^2 * l/24 * n^2 * p^2.

Where,
W- Total weight of the chain,
n- Number of supports.
If 1 support n=2.
If 2 support n=3.
Correction due to sag (Different levels).
C = Csag*cos^2 &teeta; From know source formula of sag correction is = lw^2/24p^2.

The weight here is w/m while in formula its w only thus;
SAG correction = l(w*l)^2/24p^2 ( To cancel meters of weight).
Thus option A is right. As w is given in kg / m then the above formula is correct.

But the formula will change whenever W becomes TOTAL WEIGHT. Then the formula.
= (W^2*L) ÷ 24p^2.