Radius of nth orbit of H-like particles =

0.529×n2

Z

Å =

52.9×n2

Z

pm
Radius (r1) = 1.3225 nm = 1322.5 pm =

52.9n12

Z

Radius (r2) = 211.6 pm =

52.9n22

Z

∴

r1

r2

=

1322.5

211.6

=

n12

n22

⇒ 6.25 =

n12

n22

= (

n1

n2

)2 = 6.25 ⇒

n1

n2

= √6.25 = 2.5
∴ n2 = 2, n1 = 5 thus, the transition is from 5th orbit to 2nd orbit. It belongs to Balmer series.

−

v

= 1.097 × 107(

1

22

−

1

52

) = 1.097 × 107(

1

4

−

1

25

) = 1.097 × 107×

21

100

λ =

1

− v

=

100

1.097×21×107

m = 4.34 × 10−7m = 434 × 10−9m = 434 nm
Thus, it lies in the visible region.