What is meant by ionic product of water and give its value at 25°C.

“The product of the concentration of hydrogen (H⁺) ion and hydroxide (${\mathrm{OH}}^{⊝}$) ion at any temperature in pure water (or) in any aqueous solution is known as the “Ionic product of water”.
If denoted by K_w
$\therefore {\mathrm{K}}_{\mathrm{w}}=\left[{\mathrm{H}}^{+}\right]\left[{\mathrm{OH}}^{-}\right]\text{(or) }$
${\mathrm{K}}_{\mathrm{w}}=\left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]\left[{\mathrm{OH}}^{\ominus }\right]$
$\therefore$The value of K_w at 25°c (or) 298k is $1.0\times {10}^{-14}{\mathrm{moles}}^2/{\mathrm{lit}}^2$