Which of the following has the lowest solubility?

Which of the following is the weakest base among $NaOH$,$Ca(OH)_2$,$KOH$,and $Be(OH)_2$?

Chemical $A$ is used for the removal of temporary hardness of water. Compound $A$ reacts with $Na_2CO_3$ to produce caustic soda. When $CO_2$ gas is passed through $A$,it turns milky. What is the chemical formula of $A$?

Give a detailed explanation of the oxoacid salts of alkaline earth metal elements.

Which of the following contains both calcium and magnesium?

Match the compounds in List-$I$ with their chemical formulas in List-$II$ and select the correct answer using the codes given below:
List-$I$ (Compounds) | List-$II$ (Formulas)
$(A)$ Plaster of Paris | $(i) \, CaSO_4 \cdot 2H_2O$
$(B)$ Epsomite | $(ii) \, CaSO_4 \cdot \frac{1}{2} H_2O$
$(C)$ Kieserite | $(iii) \, MgSO_4 \cdot 7H_2O$
$(D)$ Gypsum | $(iv) \, MgSO_4 \cdot H_2O$