Question

Which of the following transition will have highest emission wavelength?

Options

• n = 2 to n = 1

• n = 1 to n = 2

• n = 2 to n = 5

• n = 5 to n = 2

Answer 1

n = 5 to n = 2

Explanation:

To obtain an emission wavelength electron must transit from higher energy state to lower.

∴ For transition from n = 2 ton= 1,

`1/lambda_21 = "R" [1/1^2 - 1/2^2] = (3"R")/4`

For transition from n = 5 to n = 2,

`1/lambda_52 = "R" [1/2^2 - 1/5^2] = (21"R")/100`

`therefore 1/lambda_52 < 1/lambda_21`

`therefore lambda_52 > lambda_21`