The temperature dependence of the emf of a standard electrochemical cell is given by
`E=1.02-4.0xx10^(-5) (T-20)-9.0xx10^(-7) (T-20)^(2)`
where, T is in `.^(@)C` and E is in volts. The temperature coefficient of the emf at `30^(@)C` is :

Explanation

`(dE)/(dT)=(d)/(dT)[1.02-4.0xx10^(-5)(T-20)-8.0xx10^(-7)(T-20)^(2)]`
`=-0.4xx10^(-5)-9.0xx10^(-7)xx2(T-20)`
`=-4.0xx10^(-5)-9.0xx10^(-7)xx2(30-20)`
`=-4.0xx10^(-5)-9.0xx10^(-7)xx20`
`=-4.0xx10^(-5)-1.80xx10^(-5)=-5.8xx10^(-5)V//.^(@)C`