Question

The radii of the first Bohr orbit of $H\left(r_H\right),H{e}^{+}\left(r_{He}\right)$ and $L{i}^{2+}\left(r_{Li}^{2+}\right)$ are in the order:

• A. $r_{He}^{+}>r_H>r_{Li}^{2+}$
• B. $r_H<r_{He}^{+}<r_L{i}^{2+}$
• C. $r_H>r_{He}^{+}>r_{Li}^{2+}$
• D. $r_{He}^{+}<r_H<r_{Li}^{2+}$

Answer 1

Answer: (C)

$r_H>r_{He}^{+}>r_{Li}^{2+}$

$r=0.529\times \frac{n^2}{Z}{A}^0$

Where

r= radius of of orbit

n = prinicipal quantum number of orbit.

Z = atomic number

Now compare the $\frac{n^2}{Z}$ values of orbits for given hydrogen like atoms with that of hydrogen's first orbit to get the answer.

Hence option C is correct.