1
JEE Main 2023 (Online) 30th January Morning Shift
+4
-1

Speed of an electron in Bohr's $$7^{\text {th }}$$ orbit for Hydrogen atom is $$3.6 \times 10^{6} \mathrm{~m} / \mathrm{s}$$. The corresponding speed of the electron in $$3^{\text {rd }}$$ orbit, in $$\mathrm{m} / \mathrm{s}$$ is :

A
$$\left(1.8 \times 10^{6}\right)$$
B
$$\left(7.5 \times 10^{6}\right)$$
C
$$\left(8.4 \times 10^{6}\right)$$
D
$$\left(3.6 \times 10^{6}\right)$$
2
JEE Main 2023 (Online) 29th January Evening Shift
+4
-1
Out of Syllabus

Substance A has atomic mass number 16 and half life of 1 day. Another substance B has atomic mass number 32 and half life of $$\frac{1}{2}$$ day. If both A and B simultaneously start undergo radio activity at the same time with initial mass 320 g each, how many total atoms of A and B combined would be left after 2 days.

A
$$1.69\times10^{24}$$
B
$$3.38\times10^{24}$$
C
$$6.76\times10^{23}$$
D
$$6.76\times10^{24}$$
3
JEE Main 2023 (Online) 29th January Morning Shift
+4
-1
Out of Syllabus

If a radioactive element having half-life of $$30 \mathrm{~min}$$ is undergoing beta decay, the fraction of radioactive element remains undecayed after $$90 \mathrm{~min}$$. will be

A
$$\frac{1}{16}$$
B
$$\frac{1}{4}$$
C
$$\frac{1}{8}$$
D
$$\frac{1}{2}$$
4
JEE Main 2023 (Online) 25th January Evening Shift
+4
-1

The energy levels of an atom is shown in figure.

Which one of these transitions will result in the emission of a photon of wavelength 124.1 nm?

Given (h = 6.62 $$\times$$ 10$$^{-34}$$ Js)

A
C
B
B
C
A
D
D
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