A.) The number of electron shells increases.
Answer: 
Explanation:
Given
Initial mass 
half-life is 
At any time the left amount is given by

Expression for the Balmer series to find the wavelength of the spectral line is as follows:
1 / λ = R

Where, λ is wavelength, R is Rydberg constant, and n is integral value (4 here → Fourth level)
Substitute 1.097 x 10⁷ m⁻¹ for R and 4 for n in the above equation
1 / λ = (1.097 x 10⁷ m⁻¹)
= 0.20568 x 10⁷ m⁻¹
λ = 4.86 x 10⁻⁷ m
since 1 m = 10⁹ nm
λ = 486 nm
The volume is the space it takes up, which would be the same. The mass is measured as the weight, and the steel ball would be significantly heavier. Density is mass/volume, and if the steel has a larger mass, it will therefore have a higher density.