Question

what is pH scale what is pH value of salt formed by a weak acid and strong base and vive versa

Answer 1

potential hydrogen used to measure the extent of concentration of acid or base
for weak acid and strong base >7
for strong acid and stong base=7

Answer 2

pH value means strength( potenz) of hydrogen ions. It is way of indicating the concentration of hydrogen ions present in a solution.
It is defined as negative exponent of 10 to which it must be raised in order to express the hydrogen ion concentration of the solution in mole per litre.
Mathematically [ H^+ ( aq) = 10^-pH ]

The pH value of strong acid and weak base gives acidic solution i.e. ph less than 7
The pH value of strong base and weak acid gives basic ( alkaline) solution i.e. pH more than 7
And for weak acid and weak base is neutral