Question

Why is methyl pyridine acidic?

Answer 1

It isn't!

Explanation:

There are three methylpyridines, and all of them are weak bases (`"p"K_text(b) ≈8`).

The diagram below shows the formulas and `"p"K_text(b)` values of 4-methyl-, 3-methyl-, and 2-methylpyridine.

http://www.resonancesl.com/images/Picolinesjpg
`"p"K_text(b): color(white)(m)7.98color(white)(mmmmmmll)8.32color(white)(mmmmmmmm)8.03`
`"p"K_text(a): color(white)(m)6.02color(white)(mmmmmmll)5.68color(white)(mmmmmmmm)5.97`

However, their conjugate acids are weak acids with the `"p"K_text(a)` values shown above.