For predicting reactions, we first need to determine the phase of each of the reactants by determining their solubility. Both of our reactants are soluble so we mark them both as aqueous (abbreviated as aq in the reaction).
MgCl2(aq) + H2SO4(aq) -->
Next we need to predict the products of the reaction. Remember, that we must have one cation and one anion in each product so the only options for products are to have MgSO4 and HCl.
MgCl2(aq) + H2SO4(aq) --> MgSO4(__) + HCl(__)
Using a solubility table, we can find that MgSO4 is insoluble so we label it as (s) while HCl is soluble in water, so it is (aq).
MgCl2(aq) + H2SO4(aq) --> MgSO4(s) + HCl(aq)
The color of the solid MgSO4 is white which you can find a picture of at the link below.