Which of the following transitions will have highest emission wavelength ?

Options

A. n = 2 to n = 1
B. n = 1 to n = 2
C. n = 2 to n = 5
D. n = 5 to n = 2

Answer

D

Explanation

`1/lambda=R(1/n_(1)^(2)-1/n_(2)^(2))` where, R = Rydberg.s constant.
`R=1.01 times 10^(7) m^(-1)`
Energy is radiated out, when an electrons falls from higher orbit to lower orbit.
In n = 2 to n = 1 emission, `1/lambda_((2-1))=R times 3/4=0.75R`
In n = 5 to n = 2 emission, `1/lambda_((5-2))=R times (1/4-1/25)=(21R)/100`
`" "1//lambda_((5 " to "2))=0.21R`
`therefore lambda((2 " to "1))=1/(0.75R), lambda(5" to "2)=1/(0.21R)`
So, wavelength for the transition from n = 5 to n = 2 is highest.