What is the molecular mass of MgSO₄?

Molecular mass is the sum of all the atoms in the molecule of a compound. 

Here we are given to find the molecular mass of MgSO₄, so we will first find the Atomic mass of all the molecules so it will be Mg=24,
⇒S=32
⇒ O=16 ( here there are four oxygen atoms, so we will multiply by 4 ) 
⇒The sum of the molecules will be = $24+32+64$
= $120u$.
 Hence, the molecular mass of MgSO₄ is $120u.$