Sulphate of magnesium of the following is:

The correct option is Epsom salt.

Let us understand the chemical composition of each of the given options to determine which one represents the sulphate of magnesium:

1. Epsom Salt:
Epsom salt is the common name for the heptahydrate form of magnesium sulphate.
Its chemical formula is given by:
$${\mathrm{MgSO}}_4\cdot 7H_{2}O$$
Since it contains magnesium (${\mathrm{Mg}}^{2+}$) and sulphate (${\mathrm{SO}}_4^{2-}$) ions, it is chemically a sulphate of magnesium.

2. Gypsum:
Gypsum is a mineral composed of calcium sulphate dihydrate.
Its chemical formula is:
$${\mathrm{CaSO}}_4\cdot 2H_{2}O$$

3. Baryte:
Baryte (or barite) is a mineral consisting of barium sulphate.
Its chemical formula is:
$${\mathrm{BaSO}}_4$$

4. Galena:
Galena is the natural mineral form of lead(II) sulphide.
Its chemical formula is:
$$\mathrm{PbS}$$

Therefore, among the choices provided, Epsom salt is the sulphate of magnesium.