The radius of the forst Bohr orbit of hydrogen atom is `0.59 Å`. The radius of the third orbit of `He^(+)` will be

Options

A. `2.66 Å`
B. `1.41 Å`
C. `1.59 Å`
D. `0.705 Å`

Answer

A

Explanation

According to Bohr's theory,
`r_(n) = (n^(2)r_(1))/(Z)`
where `r_(1) = a_(0)`, the first Bohr orbit of the `H` atom. Substituting `n = 3`and` Z = 2` for `He^(+)`, we have
`r_(3) = ((3)^(2)(0.59Å))/(2)`
`2.66 Å`