1
JEE Main 2021 (Online) 25th February Morning Shift
+4
-1
Two radioactive substances X and Y originally have N1 and N2 nuclei respectively. Half life of X is half of the half life of Y. After three half lives of Y, number of nuclei of both are equal. The ratio $${{{N_1}} \over {{N_2}}}$$ will be equal to :
A
$${1 \over 8}$$
B
$${3 \over 1}$$
C
$${1 \over 3}$$
D
$${8 \over 1}$$
2
JEE Main 2021 (Online) 24th February Evening Shift
+4
-1
The de-Broglie wavelength of a proton and $$\alpha$$-particle are equal. The ratio of their velocities is :
A
4 : 2
B
4 : 3
C
4 : 1
D
1 : 4
3
JEE Main 2021 (Online) 24th February Morning Shift
+4
-1
In the given figure, the energy levels of hydrogen atom have been shown along with some transitions marked A, B, C, D and E.

The transitions A, B and C respectively represent :

A
The series limit of Lyman series, second member of Balmer series and second member of Paschen series.
B
The ionization potential of hydrogen, second member of Balmer series and third member of Paschen series.
C
The series limit of Lyman series, third member of Balmer series and second member of Paschen series.
D
The first member of the Lyman series, third member of Balmer series and second member of Paschen series.
4
JEE Main 2020 (Online) 6th September Evening Slot
+4
-1
Given the masses of various atomic particles
mp = 1.0072 u, mn = 1.0087 u, me = 0.000548 u,
$${m_{\overline v }}$$ = 0, md = 2.0141 u, where p $$\equiv$$ proton, n $$\equiv$$ neutron,
e $$\equiv$$ electron, $$\overline v$$ $$\equiv$$ antineutrino and d $$\equiv$$ deuteron. Which of the following process is allowed by momentum and energy conservation?
A
n + n $$\to$$ deuterium atom
(electron bound to the nucleus)
B
n + p $$\to$$ d + $$\gamma$$
C
p $$\to$$ n + e+ + $$\overline v$$
D
e+ + e- $$\to$$ $$\gamma$$
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