Question

how can we say that the given acid/base is strong or weak without using ph scale

Answer 1

Using litmus paper
If red litmus turns blue , then it is a base
If blue litmus turns red , then it is a red
If it do not change the colour of neither the red nor the blue litmus , then it is a neutral solution

Answer 2

because the charge of an acid is positive and the base is negattive