The activity of a solution is given by the expression: a $=c+-.$ Where the mean activity coefficient at $25C$ is given by the Debye Huckel limiting law as: $log{}_{+-}^{+-}=-0\mathrm{.}5091|Z^{+}{Z}^{-}|\sqrt[\phantom{2}]{?}.$

The ionic strength is given by the

expression: $=\frac{1}{2}({\displaystyle \underset{?}{\overset{?}{}}}{c}_i{Z}_i^2)$

Calculate the value of the log of the mean activity coefficient, $(logY+-)$ of a $0\mathrm{.}4MN{a}_{2}S{O}_4$ solution

Select one:

a$.-1\mathrm{.}018$

b$.-1\mathrm{.}115$

c$.-1\mathrm{.}668$

d$.-1\mathrm{.}577$