Which of the following hydroxides is insoluble in water?

Why does the solubility of alkaline earth metal hydroxides in water increase down the group?

The setting of Plaster of Paris is associated with which of the following?

In India,during wedding ceremonies,a green flame is observed in fireworks. Which of the following elements is responsible for this?

Which of the following statements is incorrect?

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$ :
Assertion $(A)$ : $BeCl_2$ and $MgCl_2$ produce characteristic flame.
Reason $(R)$ : The excitation energy is high in $BeCl_2$ and $MgCl_2$.
In the light of the above statements,choose the correct answer from the option given below :