Which from following decides the rate of multistep reaction?

What is minimum number of spheres required of develop a tetrahedral void?

Which from following ionic solids exhibits decrease in its solubility in water with increase of temperature?

Which from the following equations represents the relation between solubility ( $\mathrm{mol} \mathrm{~L}^{-1}$ ) and solubility product for a salt $\mathrm{B}_3 \mathrm{A}_2$ ?