Taking the Bohr radius as a₀ = 53pm, the radius of Li⁺⁺ ion its ground state, on the basis of Boh''s model, will be about

1

(a)

53pm

(b)

27pm

(c)

18pm

(d)

13pm

For the ground state, the electron in the H-atom has an angular momentum =h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,

1

(a)

because only one of these would have a minimum energy

(b)

because only one of these would have a minimum energy

(c)

angular momentum must be in the direction of spin of electron

(d)

because electrons go arround only in horizontal obits.

O₂ molecule consists of two oxygen atoms.In the molecule, nuclear force between the nuclei of the two atoms

1

(a)

is not important because nuclear forces are short-ranged

(b)

is as important as electrostatic force for binding the two atoms 

(c)

cancels the repulsive electrostatic force between the nuclei

(d)

is not important because oxygen nucleus have equal number of neutrons and protons.

Why did Thomson atom model fail?

1

(a)

This model could not explain scattering of \(\alpha \)- particle through large angles.

In Rutherford's alpha ray scattering experiment, why most of alpha particles pass through almost unscattered.

1

(a)

This is because there is a lot of empty space between the nucleus and revolving electrons in the atom.

How is impact parameter related to the scattering angle?

1

(a)

\(b=\frac { Z{ e }^{ 2 }cot\quad { \theta }/{ 2 } }{ 4\pi { \epsilon }_{ 0 }\left( \frac { 1 }{ 2 } m{ v }^{ 2 } \right) } \)

Can a hydrogen atom absorb a photon whose energy exceeds its binding energy?

1

(a)

Yes, it can absorb.

Write the relation for (i) the distance of closest approach and (ii)  impact parameter.

1

(a)

\((i)\quad { r }_{ 0 }=\frac { Ze(2e) }{ 4\pi { \epsilon }_{ 0 }\left( \frac { 1 }{ 2 } m{ v }^{ 2 } \right) }\)
\( \\ (ii)\quad b=\frac { 1 }{ 4\pi { \epsilon }_{ 0 } } \frac { Z{ e }^{ 2 }cot\quad { \theta }/{ 2 } }{ \left( \frac { 1 }{ 2 } m{ v }^{ 2 } \right) } \)

what conclusions were drawn from the observation in which few alpha-particle were seen rebounding from gold foil?

1

(a)

The entire positive charge and the mass were concentrated at one place inside the atom, called the nucleus.

which observation led to the conclusion in the \(\alpha\)-particle scattering exp. That atom has vast empty space?

1

(a)

A larger number of alpha particle went through undeflected

Two nuclei have mass numbers in the ratio 1:8.What is the ratio of their nuclear radii?

1

(a)

\(R={ R }_{ 0 }{ A }^{ 1/3 },{ R }_{ 1 }/{ R }_{ 2 }={ A }_{ 1 }^{ 1/3 }/{ A }_{ 2 }^{ 1/3 }=1,^{ 1/3 }/27_{ 1/3 }=1/3\)

which have greater ionizing power:α-particles or \(\beta\)-particles?

1

(a)

\(\alpha\) - particles have more ionizing power than \(\beta\) - particles  

The half life of a radioactive substance in 30 days. What is the time taken for ¾ of its original mass to disintegrate?

1

(a)

N/No = (1/2)ⁿ
t = 2T = 2 x 30 = 60 days