Why is +l-effect of t-butyl group greater than that of isopropyl group?

Explanation

Inductive effect due to the presence to the presence of electron repelling group, attached to the one end of a saturated carbon chain is called +I effect. As the electron repelling groups increases, their inductive effect increases. Based on this, we can say ethyl group (having `-CH_(2)CH_(3)`) has more inductive effect than methyl `(-CH_(3))` group. In the same way, tertiary group (having three methyl groups, `(CH_(3))_(3)C`- has more inductive effect than isopropyl group. Thus, the order of +I effect of the alkyl groups will be:
`(CH_(3))_(3) C- gt (CH_(3))_(2)CH - gt - CH_(2) CH_(3)gt - CH_(3)`
`{:("t-butyl",gt,"isopropyl",gt,"ethyl",gt,"methyl"),(3,gt,2,gt,1,,):}`