1
JEE Main 2019 (Online) 10th April Morning Slot
+4
-1
Two radioactive materials A and B have decay constants 10$$\lambda$$ and $$\lambda$$, respectively. It initially they have the same number of nuclei, then the ratio of the number of nuclei of A to that of B will be 1/e after a time :
A
1/9$$\lambda$$
B
11/10$$\lambda$$
C
1/10$$\lambda$$
D
1/11$$\lambda$$
2
JEE Main 2019 (Online) 9th April Evening Slot
+4
-1
A He+ ion is in its first excited state. Its ionization energy is :-
A
13.60 eV
B
6.04 eV
C
48.36 eV
D
54.40 eV
3
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
4
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
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