NEET Chemistry Questions: Structure of Atom

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A near U.V. photon of 300 nm is absorbed by a gas and then remitted as two photons. One photon is red with wavelength760 nm. Hence wavelength of the second photon is




$ E - = E_1 + E_2 now E = { hc \over \lambda} $ $ \therefore { 1 \over \lambda } = { 1 \over \lambda_1 } + { 1 \over \lambda_2 } $
The transition in $He^+$ ion that would have the same wave number as the first Lyman line in hydrogen spectrum is




$ \bar \nu = R Z ^2 [ { 1 \over n ^2 _1 } - { 1 \over n ^2 _f } ]cm ^ {-1} $ $ \bar \nu_H = R [ { 1 \over n ^2 _1 } - { 1 \over n ^2 _f } ]cm ^ {-1} $ $ \bar \nu_{He} = R Z ^2 [ { 1 \over n ^2 _1 } - { 1 \over n ^2 _f } ]cm ^ {-1} $
The work function of a metal is 4.2 eV. If radiations of $2000 A ^\circ $ fall on the metal then the kinetic energy of the fastest photo electron is




The work function of a metal is the minimum energy required to remove an electron from the metal surface. If the energy of the incident photon (E = hc/λ) is greater than the work function, the excess energy is given to the emitted electron as kinetic energy. Given: Work function = 4.2 eV, λ = 2000 Å = 2000 × 10^-10 m. Kinetic energy of the fastest photoelectron = hc/λ - Work function = (6.63 × 10^-34 × 3 × 10^8) / (2000 × 10^-10) - (4.2 × 1.6 × 10^-19) = 3.2 × 10^-19 J.
The ratio of the radil of the first three Bohr orbit in H atom is




$ r_n = n^2 a_0 i.e. r \alpha n^2 r1 : r2 : r3 = 1^2 : 2^2 : 3^2 = 1 : 4 : 9 $
The momentum of a particle associated with de-Broglie’s wave length of $ 6 A ^\circ $ is




No explanation available.
Frequency of matter wave is equal to v = frequency, v = velocity of particle




$ \lambda = { h \over mv } v = \lambda v \therefore \lambda = { v \over \nu } \therefore { v \over \nu } = { h \over mv } \therefore \nu = { mv^2 \over h } = { 2 K.E \over h } ( K.E = { 1 \over 2} mv ^2) $
The mass of one mole of electron is




No explanation available.
For the electronic transition from n = 2 to n = 1 which one of the following will produce shortest wave length?




For the transition from n=2 to n=1, the wavelength emitted is inversely proportional to the nuclear charge (Z). The higher the nuclear charge, the shorter the wavelength emitted. Among the given options, Li^(2+) has the highest nuclear charge (Z=3), so it will emit the shortest wavelength for the n=2 to n=1 transition.
The energy required to dislodge electron from excited isolated H atom (IE = 13.6eV) is




No explanation available.
Velocity of electron in the first orbit of H-atom is compared to that of velocity of light is approximately




The velocity of an electron in the first orbit (n=1) of a hydrogen atom is approximately 1/137 times the speed of light. This value is known as the fine-structure constant and arises from the relativistic correction to the Bohr model of the hydrogen atom.
How many electrons in Cu atom have (n + ) = 4




No explanation available.
For a certain particle, it is found that uncertainty 1840 in velocity is reciprocal of uncertainty in position This implies that




No explanation available.
Suggest two transitions in hydrogen spectrum for which wave number ratio is 108:7




The wave number ratio of 108:7 corresponds to the transitions 2 → 1 and 4 → 3 in the hydrogen spectrum. This can be calculated using the Rydberg formula, which relates the wavenumber to the energy levels involved in the transition.
The ratio of K.E. to P.E. of an electron in Bohr orbit of H like species is




$ K.E = { Ze ^ 2 \over 2 r } P.E = { Ze ^2 \over r } \therefore {K.E \over P.E} = { 1/2 \over -1 } = -1.2 $
For particles having same KE., the de-broglie wavelength is




No explanation available.