Doubtclip is an AI tutor that turns any homework or exam doubt into a step-by-step whiteboard video lesson with diagrams, formulas, and voice explanation.

Which subjects and exams does it support?

It supports Physics, Chemistry, Mathematics/Calculus and related STEM doubts for school boards, JEE, NEET, and global high-school / undergrad practice.

How do I get a video solution?

Upload a photo of the question or paste the text, sign in, and Doubtclip generates a whiteboard-style explanation video you can watch and share.

Is Doubtclip available worldwide?

Yes. Doubtclip is a web app for students globally. Lessons are available in English and Hinglish.

Atoms & Nuclei

JEE Main level, numerical answer, medium

46 of 239

Question 46 of 239

The radius of ${2}^{nd}$ orbit of ${He}^{+}$ of Bohr's model is ${r}_{1}$ and that of fourth orbit of ${Be}^{3+}$ is represented as ${r}_{2}.$ Now the ratio $\dfrac{{r}_{2}}{{r}_{1}}$ is $x:1.$ The value of $x$ is _____.

Show answer and solution

Answer: 2

The formula to calculate the radius

\left(r\right)

of any

{n}^{th}

Bohr's orbit is given by

r={r}_{0}\dfrac{{n}^{2}}{Z}...\left(1\right)

where,

{r}_{0}

is Bohr's radius,

n

is the principal quantum number and

Z

is the atomic number.
Thus, for Helium ion,

\begin{matrix}{r}_{1} & = & {r}_{0}\dfrac{{2}^{2}}{2} \\ & = & 2{r}_{0}...\left(2\right)\end{matrix}

And, for the Beryllium ion,

\begin{matrix}{r}_{2} & = & {r}_{0}\dfrac{{4}^{2}}{4} \\ & = & 4{r}_{0}...\left(3\right)\end{matrix}

Divide equation (3) by equation (2) to obtain the required ratio.

\begin{matrix}\dfrac{{r}_{2}}{{r}_{1}} & = & \dfrac{4{r}_{0}}{2{r}_{0}} \\ & = & 2\end{matrix}

Hence,

x=2

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

See it move: Atoms: Rutherford, Bohr and X-rays simulationDrag the sliders and watch the numbers in this question change.Revise Modern Physics firstFormula sheet, solved examples and the traps students fall into.

More Physics practice

JEE Main Physics practice question on Atoms & Nuclei (Bohr's Atomic Model), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.

The radius of 2nd{2}^{nd}2nd orbit of He+{He}^{+}He+ of Bohr's model is r1{r}_{1}r1​ and that of fourth orbit of Be3+{Be}^{3+}Be3+ is represented as r2.{r}_{2}.r2​. Now the ratio r2r1\dfrac{{r}_{2}}{{r}_{1}}r1​r2​​ is x:1.x:1.x:1. The value of xxx is _____.

JEE Main question paper PDF

More Physics practice

The radius of ${2}^{nd}$ orbit of ${He}^{+}$ of Bohr's model is ${r}_{1}$ and that of fourth orbit of ${Be}^{3+}$ is represented as ${r}_{2}.$ Now the ratio $\dfrac{{r}_{2}}{{r}_{1}}$ is $x:1.$ The value of $x$ is _____.