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12th Grade > Physics

ATOMS AND NUCLEI MCQs

Atoms, Nuclei (12th Grade)

Total Questions : 60 | Page 1 of 6 pages
Question 1. Hydrogen atom emits blue light when it jumps from n = 4 energy level to the n = 2 level. Which colour of light would the atom emit when it changes from the n = 5 level to the n = 2 level?
 
  1.    Red
  2.    Yellow
  3.    Green
  4.    Violet
 Discuss Question
Answer: Option D. -> Violet
:
D
E5E1=ΔE51
ΔE51>ΔE42 Violet color has more energy than Blue color while all colors in the option have less energy than Blue color
Violet
Question 2. After two hours, one- sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is
  1.    15 minutes
  2.    30 minutes
  3.    45 minutes
  4.    1 hour
 Discuss Question
Answer: Option B. -> 30 minutes
:
B
NN0=(12)tT(116)=(12)2T(12)4=(12)2T
T = 0.5 hour = 30 minutes.
Question 3. If Avogadro's number is 6×1023 then the number of protons, neutrons and electrons in 14 g of 6C14 are respectively 
  1.    36×1023,48×1023,36×1023  
  2.    36×1023,36×1023,36×1021
  3.    48×1023,36×1023,48×1021
  4.    48×1023,48×1023,36×1021
 Discuss Question
Answer: Option A. -> 36×1023,48×1023,36×1023  
:
A
Since the number of protons, neutrons and electrons in an atom of 6C14 are 6, 8 and 6 respectively. As 14 gm of 6C14 contains 6×1023 atoms, therefore the numbers of protons, neutrons and electrons in 14 gm of 6C14 are 6×6×1023,=36×1023,8×6×1023=48×1023,6×6×1023=36×1023.
Question 4. On the bombardment of a neutron with Boron. α-particle is emitted and product nuclei formed is
  1.    6C12
  2.    3Li6
  3.    3Li7  
  4.    4Be9
 Discuss Question
Answer: Option C. -> 3Li7  
:
C
5B10+0n13Li7+2He4.
Question 5. The radius of the first orbit of hydrogen in 0.528˙A. The radius of second orbit of hydrogen is
  1.    4.752˙A
  2.    2.112˙A
  3.    0.071˙A
  4.    0.142˙A
 Discuss Question
Answer: Option B. -> 2.112˙A
:
B
rnn2
r2r1=2212=4
r2=4r
=4×0.528
=2.112˙A
Question 6. An electron in ground state of hydrogen has an angular momentum L1 and an electron in the first excited state of Lithium has an angular momentum L2. Then 
  1.    L1=L2
  2.    L1=4L2
  3.    L1=L22
  4.    L1=2L2
 Discuss Question
Answer: Option C. -> L1=L22
:
C
L=nh2π Hence L1n1
L2n2
L2L1=n2n1=21 L1=L22
Question 7. The circumference of first orbit of hydrogen atom is ‘s’. Then the Broglie wavelength of electron in that orbit is
  1.    S2
  2.    2S
  3.    S
  4.    3S
 Discuss Question
Answer: Option C. -> S
:
C
2πrn=nλ
n=1
2πr1=λ
λ=2πr1=S
Question 8. The ratio of wave length of first line of Lyman series to the first line of Balmer series is
  1.    1 : 4
  2.    5 : 27
  3.    27 : 20
  4.    20 : 27
 Discuss Question
Answer: Option B. -> 5 : 27
:
B
λ1=43R λ2=365R
λ1λ2=43×536=527
Question 9. Energy levels A,B,C of an atom are shown below
Energy Levels A,B,C Of An Atom Are Shown BelowIf EA<EB<...
If EA<EB<EC, the wavelength emitted due to transistion from C to A is λ3then correct statements of the following is
 
  1.    λ3=λ1+λ2
  2.    λ3=λ1×λ2λ2+λ1
  3.    λ1+λ2+λ3=0
  4.    λ23=λ21+λ22
 Discuss Question
Answer: Option B. -> λ3=λ1×λ2λ2+λ1
:
B
ECA=ECB+EBA
hcλ3=hcλ1+hcλ2
λ3=λ1×λ2λ2+λ1
Question 10. In the Bohr's hydrogen atom model, the radius of the stationary orbit is directly proportional to (n = principle quantum number)
  1.    n−1
  2.    n
  3.    n−2
  4.    n2
 Discuss Question
Answer: Option D. -> n2
:
D
Bohr radius r=0n2h2πZme2;rn2

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