1
JEE Main 2019 (Online) 9th April Morning Slot
+4
-1
Taking the wavelength of first Balmer line in hydrogen spectrum (n = 3 to n = 2) as 660 nm, the wavelength of the 2nd Balmer line (n = 4 to n = 2) will be :
A
642.7 nm
B
488.9 nm
C
889.2 nm
D
388.9 nm
2
JEE Main 2019 (Online) 8th April Evening Slot
+4
-1
The ratio of mass densities of nuclei of 40Ca and 16O is close to :-
A
1
B
5
C
0.1
D
2
3
JEE Main 2019 (Online) 8th April Morning Slot
+4
-1
Radiation coming from transitions n = 2 to n = 1 of hydrogen atoms fall on He+ ions in n = 1 and n = 2 states. The possible transition of helium ions as they absorb energy from the radiation is :
A
n = 1 $$\to$$ n = 4
B
n = 2 $$\to$$ n = 5
C
n = 2 $$\to$$ n = 4
D
n = 2 $$\to$$ n = 3
4
JEE Main 2019 (Online) 12th January Evening Slot
+4
-1
In a radioactive decay chain, the initial nucleus is $${}_{90}^{232}$$Th. At the end there are 6 $$\alpha$$-particles and 4 $$\beta$$-particles which are emitted. If the end nucleus is $${}_Z^A$$X, A and Z are given by :
A
A = 208; Z = 80
B
A = 208; Z = 82
C
A = 200; Z = 81
D
A = 202; Z = 80
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