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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?

Solution

(c)

Radius of orbit (r)=(n^2 h^2)/(4Ï€^2 me^2 )×1/Z

In it h,Ï€,m and e are constants, so after substituting these values, we get

r=(0.529n^2)/Z â„«

Z=1 for H

∴ r_H=(0.529n^2)/1 â„« …(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.

(c)

Radius of orbit (r)=(n^2 h^2)/(4Ï€^2 me^2 )×1/Z

In it h,Ï€,m and e are constants, so after substituting these values, we get

r=(0.529n^2)/Z â„«

Z=1 for H

∴ r_H=(0.529n^2)/1 â„« …(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 â„« wavelength radiation to that of 4000 â„« radiation is

Solution

Part D

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

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

(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

Solution

(b) Î³-particles are neutral, hence they do not get repelled by the electrostatic force of nuclei

(b) Î³-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

Solution

(d) _13^29 Al→ _13^27 Al+2 _0^1 n

(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

Solution

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

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

**Q7.**A sievert is

Solution

Part D

Part D

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

Solution

(a) Radioactive disintegration is a nuclear process

(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

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

(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

Solution

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

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