Precipitation of $CaF_2$ $(K_{sp} = 1.7 \times 10^{-10})$ occurs when equal volumes of which of the following are mixed?

An acidified solution of $0.05 \ M \ Zn^{2+}$ is saturated with $0.1 \ M \ H_2S$. What is the minimum molar concentration $(M)$ of $H^{+}$ required to prevent the precipitation of $ZnS$? Use $K_{sp}(ZnS) = 1.25 \times 10^{-22}$ and overall dissociation constant of $H_2S$,$K_{NET} = K_1 K_2 = 1 \times 10^{-21}$.

The salt having the least solubility in water is

The solubility product of $Ni(OH)_2$ at $298 \ K$ is $2 \times 10^{-15} \ mol^3 \ dm^{-9}$. The $pH$ value of its aqueous and saturated solution is

Observe the following solutions:
$(i)$ $1 \ L$ of $10^{-6} \ M \ AgNO_3$
$(ii)$ $1 \ L$ of $10^{-7} \ M \ AgNO_3$
$(iii)$ $1 \ L$ of $10^{-9} \ M \ AgNO_3$
$(iv)$ $1 \ L$ of $10^{-3} \ M \ AgNO_3$
$(v)$ $1 \ L$ of $10^{-5} \ M \ NaCl$
Which of the above two solutions when mixed will give a white precipitate,$AgCl$?
$(Given \ K_{sp} \ of \ AgCl = 1 \times 10^{-10})$

Two salts $A_2X$ and $MX$ have the same value of solubility product of $4.0 \times 10^{-12}$. The ratio of their molar solubilities i.e. $\frac{S(A_2X)}{S(MX)} = \dots$ (Round off to the Nearest Integer).