What is wrong with the name 1-t-butyl-2-methylpropane?

Explanations:- While naming a carbonic compound then first of all we select the longest carbon chain. If we draw the structure for the given name then parent carbon chain(propane) has three carbons. There is a methyl at second carbon and tertiary butyl group at first carbon. This tertiary butyl group changes the parent carbon. In actual, the parent chain would have five carbons and we have three methyl groups in total, two methyl groups at second carbon and one methyl group at fourth carbon.

So, the correct name will be 2,2,4-trimethylpentane.

The image is shown below.