Arrange the following compounds in increasing order of their property as indicated:
$(i)$ Acetaldehyde,Acetone,Di-tert-butyl ketone,Methyl tert-butyl ketone (reactivity towards $HCN$)
$(ii)$ $CH_3CH_2CH(Br)COOH$,$CH_3CH(Br)CH_2COOH$,$(CH_3)_2CHCOOH$,$CH_3CH_2CH_2COOH$ (acid strength)
$(iii)$ Benzoic acid,$4$-Nitrobenzoic acid,$3,4$-Dinitrobenzoic acid,$4$-Methoxybenzoic acid (acid strength)

(A) $(i)$ Reactivity towards $HCN$ depends on the electrophilicity of the carbonyl carbon and steric hindrance. As the number of alkyl groups increases,both steric hindrance and $+I$ effect increase,reducing reactivity. The order is: $\text{Di-tert-butyl ketone} < \text{Methyl tert-butyl ketone} < \text{Acetone} < \text{Acetaldehyde}$.
$(ii)$ Acid strength increases with the presence of electron-withdrawing groups ($-I$ effect) and decreases with electron-donating groups ($+I$ effect). The $-I$ effect of $Br$ decreases with distance. The order is: $(CH_3)_2CHCOOH < CH_3CH_2CH_2COOH < CH_3CH(Br)CH_2COOH < CH_3CH_2CH(Br)COOH$.
$(iii)$ Electron-withdrawing groups $(-I, -M)$ increase acid strength,while electron-donating groups $(+M, +I)$ decrease it. The order is: $4\text{-Methoxybenzoic acid} < \text{Benzoic acid} < 4\text{-Nitrobenzoic acid} < 3,4\text{-Dinitrobenzoic acid}$.