Video narration
Why isn't trimethylamine the most basic of these four in water? When you draw a Lewis structure, the nitrogen lone pair is where a proton attaches. Basicity compares how ready that pair is to accept one. Each methyl group pushes electron density toward nitrogen, making its lone pair more ready to accept a proton. So if donation were the whole story, trimethylamine should win. But water changes the comparison. After a proton attaches, water also stabilizes the positively charged amine. The different methylamines interact with water differently, so electron donation is only part of the result. The balance decides which lone pair belongs to the strongest base in solution. For ammonia, methylamine, dimethylamine, and trimethylamine in water, the increasing order is ammonia, trimethylamine, methylamine, then dimethylamine. So no: trimethylamine is not strongest. Dimethylamine is, because water matters alongside the lone pair.