Arrangethe following compounds in increasing order of their property as indicated :
(i) Acetaldehyde, Acetone, Di - tery - butyl ketone, Methyl tert - butyl ketone (reactivity towards HCN)
CH_(3)CH_(2)CH(Br)CH_(2)COOH,(CH_(3))_(2)CHCOOH,CH_(3)CH_(2)CH_(2)COOH(" acid strength").
(iii) Benzoic acid, 4 - Nitrobenzoic acid, 3, 4 - Dinitrobenzoic acid, 4 - Methoxybenzoic acid (acid strength).

Solution :(i) The reactivity towards HCN addition decreases as the `+I-` effect of the ALKYL group increases and the steric hindrance to the nucleophilic attack by `CN^(-)` increases. Di - tert - butyl KETONE offers the MAXIMUM steric hindrance and has maximum `+I-` effect. Therefore, it has the least reactivity.

tery - Butylmethyl ketone also offers a lot of steric hindrance and `+I-` effect. But, it is a more reactive than Di - tery - butyl ketone. Acetaldehyde is most reactive.
Order of reactivity is :
`"Di - tery - butyl ketone "lt "tert - Butyl methyl ketone" lt "Acetone" lt "Acetaldehyde"`
2)CHCOOH` is a weaker acid than `CH_(3)CH_(2)CH_(2)COOH`.
Further `-I-` effect decreases with distance, therefore, `CH_(3)CH_(2)CH(Br)COOH` is a STRONGER acid than `CH_(3)CH(Br)CH_(2)COOH`. Thus, the overall acid strength increases in the order :
`CH_(3)-overset(CH_(3))overset("|")"CH"-COOH lt CH_(3)CH_(2)CH_(2)-COOH lt CH_(3)-underset (Br)underset(|)CH-CH_(2)-COOH lt CH_(3)-CH_(2)-underset(Br)underset(|)CH-COOH`
(iii) Since electron - donating groups decrease the acid strength, 4 - methoxybenzoic acid is a weaker acid than benzoic acid.
Since electron - withdrawing group increase the acid strength, 4 - nitrobenzoic acid and 3, 4 - dinitrobenzoic acids are stronger acids than benzoic acid. Further due to the presence of an additional `NO_(2)` group at m - position w.r.t. `COOH` group, 3, 4 - dinitrobenzoic acid is a stronger acid than 4 - nitrobenzoic acid. Thus, the overall acid strength increases in the order :
`"4 - Methoxybenzoic acid" lt " Benzoic acid " lt "4 - Nitrobenzoic acid "lt 3, 4 - "Dinitrobenzoic acid."`