STRUCTURE OF ATOM Quiz-15

Chemistry Aptitude Quiz

Dear Readers,

IIT JEE exam which consists of JEE Main and JEE Advanced is one of the most important entrance exams for engineering aspirants. The exam is held for candidates who are aspiring to pursue a career in the field of engineering and technical studies. Chemistry is important because everything you do is chemistry! Even your body is made of chemicals. Chemical reactions occur when you breathe, eat, or just sit there reading. All matter is made of chemicals, so the importance of chemistry is that it's the study of everything..

Q1. Which hydrogen like species will have same radius as that of Bohr orbit hydrogen atom?

•  n=2,Li^(2+)
•  n=2,Be^(3+)
•  n=2,He^+
•  n=3,Li^(2+)

Solution
(c)
Radius of orbit (r)=(n^2 h^2)/(4π^2 me^2 )×1/Z
In it h,π,m and e are constants, so after substituting these values, we get
r=(0.529n^2)/Z Å
Z=1 for H
∴ r_H=(0.529n^2)/1 Å …(i)
The transition from n=2 to n=1 in H-atom will have the same wavelength as the transition from n=4 to n=2 in He^+ ion.

Q2.The ratio of the energy of a photon of 2000 Å wavelength radiation to that of 4000 Å radiation is

•  1⁄4
•  4
•  1⁄2
•  2

Solution
Part D

Q3.  The energy of an electron in the first Bohr orbit of H atom is -13.6 eV. The possible energy value(s) of the excited state (s) for electrons in Bohr orbits of hydrogen is/are

•  -3.4 eV
•  -4.2 eV
•  -6.8 eV
•  +6.8 eV

Solution
(a)
E_n=(-13.6)/n^2 Z^2 eV
For n=2, for H atom,
E=(-13.6)/2^2 1^2 eV=-3.4 eV
Other values cannot be obtained for n=3,4,5,6 etc

Q4.   Neutrons are more effective projectiles than protons because they

•  Are attracted by the nuclei
•  Are not repelled by the nuclei
•  Travel with high speed
•  None of above

Solution

(b) γ-particles are neutral, hence they do not get repelled by the electrostatic force of nuclei

Q5. _13^27 Al is a stable isotope. _13^27 Al is expected to disintegrate by

•  α-emission
•  β-emission
•  Positron emission
•  Neutron emission

Solution
 (d) _13^29 Al→ _13^27 Al+2 _0^1 n

Q6. If two light nuclei are fused together in nuclear reaction, the average energy per nucleon

•  Increases
•  Decreases
• Cannot be determined
•  Remains same

Solution
(b) Due to mass defect some energy is lost as heat energy

Q7.A sievert is

•  The amount of radiation that produces 2.1×10^9units of charge in one cm^3 of air
•  A unit used to measure the amount of radiation absorbed per gram of tissue
•  A unit that allows both for the energy and the penetrating power of different types of radiation
•  The SI unit for radiation absorbed

Solution
Part D

Q8.Radioactive disintegration differs from a chemical change in being a/an

•  Nuclear process
•  Exothermic change
•  Spontaneous process
•  First order kinetics

Solution
(a) Radioactive disintegration is a nuclear process

Q9.If Hund’s rule is not followed, magnetic moment of Fe^(2+),Mn^⊕, and Cr all having 24 electrons will be in order

•  Fe^(2+)< Mn^⊕< Cr
•  Fe^(2+)=Cr< Mn^⊕
•  Fe^(2+)=Mn^⊕< Cr
•  Mn^(2+)=Cr< Fe^(2+)

Solution
(b)
Fe^(2+):[Ar]3d^6unpaired electron=0
Mn^(2+):[Ar]3d^5 4s^1 unpaired electron=2
Cr:[Ar]3d^4 s^2 unpaired electron=0
If Hund’s rule is not followed

Q10. The nuclear reaction ( _5^10 B+ _0^1 n→ _3^7 Li+ _2^4 He) is of the type

•  n,p
•  n,β
•  n,α
• α,n

Solution
(c) It capture neutrons and emits α-particle Thus, (n,α) _5^10 B □((→┴( α ↓ emitted))┬(n ↑ captured) ) _3^7 Li

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