If the density of the whole block is 7.75 g/mL, then the density of half of it is also 7.75 g/mL. (a)
The density of any substance is the same ... mass/volume ... no matter how big or small the sample is.
If the substance is pure, then its density is always the same. It doesn't matter whether your sample is a tiny drop in the middle of your finger-nail or a super-tanker full of it.