The molar ionic conductivities of `NH_(4)^(+) annd OH^(-)` at infinite dilution are 72 and 198 `ohm^(-1)cm^(2)`, respectively, the molar conductivity of a centinormal `NH_(4)OH` solution aththe same temperature is found to be 9 `ohm^(-1)cm^(2)`. The percentage dissociation of `NH_(4)OH` at this concentration will be

Options

A. `33%`
B. `7.14 %`
C. `12.5%`
D. `4.54 %`

Answer

C

Explanation

`Lambda^(@) (NH_(4)OH) = lambda_(NH_(4)^(+))^(@) + lambda_(OH^(-))^(@)`
`= 72 + 198 = 270 ohm^(-1) cm(2)`
`alpha = Lambda//Lambda^(@) = 9//270 = 1//30 = 0.0333`
`% alpha = 3.33 %`