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The ground state electronic configuration of Cr is [Ar] 4s 1 3d 5 or 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 The 19th electron is 4s 1 ∴ For 4s 1 electron n = 4, l = 0, m = 0, s = +1/2 or -1/2.

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Structure of Atom

Short Answer Type

251.

Write the value of n, l and m for the electron with the highest energy in sodium atom (Z =11).

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252.
With the help of ground state electronic configuration of element Cr(Z= 24), deduce the possible values of four quantum numbers for the 19th electron of Cr.

The ground state electronic configuration of Cr is
[Ar] 4s¹ 3d⁵ or 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵
The 19th electron is 4s¹
∴ For 4s¹ electron
n = 4, l = 0, m = 0, s = +1/2 or -1/2.

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253. Calculate the wavelength, frequency and wave number of light wave whose period is 2.0 x 10^-10 s.

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Long Answer Type

254. How many neutrons and protons are there in the following nuclei?

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Short Answer Type

255. Calculate the energy required for the process.
He⁺(g) → He²⁺ (g) + e^-
The ionization energy for the H atom in the ground state is 2.18 x 10^-18 J atom^-1

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256. If the diameter of a carbon atom is 0.15 nm, calculate the number of carbon atoms which can be placed side by side in a straight line across length of scale of length 20 cm long.

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Multiple Choice Questions

257.

A stream of electrons from a heated filament was passed between two charged plates kept at a potential difference V esu. If e and m are charge and mass of an electron, respectively, then the value of h/λ (where λ is wavelength associated with electron wave) is given by:

2meV
$square root of mev$
$square root of 2 meV end root$
$square root of 2 meV end root$

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258.

Which of the following is the energy of a possible excited state of hydrogen?

+13.6 eV
-6.8 eV
-3.4 eV
-3.4 eV

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259.

The correct set of four quantum numbers for the valence electrons fo rubidium atom (Z = 37) is

5,0,0, +1/2
5,1,0,6+1/2
5,1,1,+1/2
5,1,1,+1/2

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260.

Energy of an electron is given by
E =- 2.178 x 10^-18 J $open parentheses straight Z squared over straight n squared close parentheses$
Wavelength of light required to excite an electron in a hydrogen atom from level n =1 to n=2 will be (h=6.62 x 10³⁴ Js and c = 3.0 x 10⁸ ms^-1)