Question

List any 2 past participles in which last letter is doubled??

Answer 1

Many do. Here are some examples:

Rubbing

Padding

Bragging

Humming

Running

Rapping

Warring

Batting

Revving

I think the basic rule is that you need to double the last letter if not doing so would significantly change the pronunciation (and possibly the meaning).

For example, you do not want to drop the extra p in rapping.