The molar ionic conductivities of `NH_4^+` and `OH^(-)` at infinite dilution are 72 and 198 `ohm^(-1)` `cm^(2)` respectively. The molar conductivity of a centinormal `NH_4OH` solution at the same temperature is found to be 9 `ohm^(-1)` `cm^(2)` . The percentage dissociation of `NH_4OH` at this concentration will be

Options

A. 0.0333
B. 0.0714
C. 0.125
D. 0.0454

Answer

A

Explanation

`Lambda_(m(NH_4OH))^@=lambda_(NH_4^+)^@+lambda_(OH^(-))^@`
=72+198=270 `ohm^(-1)cm^2`
`alpha=Lambda_m^c/Lambda_m^@=9/270=1/30=3.33%`