Question

Why proton is always positive charge

Answer 1

A proton being positively charged is just a convention. It is not the usual “positive” you think about. We found out that there can be three kinds of charges- two of which attract to each other and the third is “neutral” to the. So, we decided to name them positive, negative and neutral. We just decided to give positive charge to proton. We could have given negative charge to proton too and it wouldn't have changed any physics.