1
JEE Main 2021 (Online) 24th February Morning Slot
MCQ (Single Correct Answer)
+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.
2
JEE Main 2020 (Online) 6th September Evening Slot
MCQ (Single Correct Answer)
+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- $$\to$$ $$\gamma$$
3
JEE Main 2020 (Online) 5th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
A radioactive nucleus decays by two different processes. The half life for the first process is 10 s and that for the second is 100 s. The effective half life of the nucleus is close to :
A
12 sec
B
9 sec
C
55 sec
D
6 sec
4
JEE Main 2020 (Online) 5th September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Activities of three radioactive substances A, B and C are represented by the curves A, B and C, in the figure. Then their half-lives
$${T_{{1 \over 2}}}\left( A \right)$$ : $${T_{{1 \over 2}}}\left( B \right)$$ : $${T_{{1 \over 2}}}\left( C \right)$$ are in the ratio :
A
3 : 2 : 1
B
2 : 1 : 1
C
4 : 3 : 1
D
2 : 1 : 3
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