Solid is a substance that is solid rather than liquid. In solids particles are packed closely together and are not free to move about within the substance.
Liquid is a substance that moves freely but of constant volume,like having a contensy of water or oil.
We arrange oxoacids to decrease the intensity of acids in this question. Or we may conclude all this from strongest to weakest acids they order oxoacids, that's why above given order is correct.
