For a two-hinged arch, if one of the supports settles down vertically, then the horizontal thrust

option b is correct.

Good explain

Horizontal thrust is not much affected by vertical movement of support as compared to side movements. When ur support settles horizontally, Thrust decreases bcz of the temperature stresses. And bending moment increases as well.
Is ko counter krny k lye 2 hinged mein ik support ko roller bnadety hain, aor arch ki rise ko increase kar dety hain.