What is the dissociation constant of water at $25^{\circ}C$?

The $pH$ of a sample of vinegar is $3.76$. Calculate the concentration of hydrogen ion in it in $mol \ dm^{-3}$?

$2$. Given below are two statements:
Statement $I$: The changes in $pH$ with temperature are so small that we often ignore them.
Statement $II$: When the hydrogen ion concentration changes by a factor of $100$,the $pH$ changes by one unit.
In the light of the above statements,identify the correct answer from the options given below:

The concentration of hydronium $({H_3}{O^{+}})$ ion in pure water at $298 \ K$ is:

The $pH$ of a solution is the negative logarithm to the base $10$ of its hydrogen ion concentration in:

The standard Gibbs energy change in the reaction $H_2O \rightleftharpoons H^{+} + OH^{-}$ at $25\ ^oC$ is.....$kJ/mol$.