Hello Aashish, Greetings!

We know according to equation of gases:

PV=nRT

now take log both side

log(PV)=log (nRT)

logP +logV=log (nRT)

logP= (-1) logV +log (nRT)

In question, given temperature is constant and mass is also constant hence mole is constant , its mean nRT is constant .

just like y=mx+c where

y =logP, x=logV, c=log (nRT) and m= -1 here m is slope of equation

So, slope = -1 is required ananswer.

Thank you.