A solid is suspended in a liquid. If the liquid is heated, the solid (assume the solid expansion is negligible)

Let T is tension in the string which gives apparent weight.

$\mathrm{T}=\mathrm{Mg}-{\mathrm{F}}_{\mathrm{B}}$

$\mathrm{Buyoncy} \mathrm{force} {\mathrm{F}}_{\mathrm{B}} ={\mathrm{V}}_{\mathrm{S}}{\mathrm{\rho }}_{\mathrm{L}}\mathrm{g}$, 

On heating density of liquid decreases. Weight of solid and volume of solid will not change. Buoyancy force decreases and  apparent weight increases.