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. 0.0333
B. 0.0714
C. 0.125
D. 0.0454

Answer

A

Explanation

By Kahlrausch's law,
`wedge_(m)^(oo)(NH_(4)OH)=lamda^(prop)(NH_(4)^(+))+lamda^(prop)(OH)`
`=72+198=270ohm^(-1)cm^(2)`
`alpha=wedge_(m)^(c)//wedge_(m)^(prop)=9//270`
`=1//30=0.0333%`
`%alpha=3.33%`