Chemistry

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans: Option (iv)

Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube. As per the result obtained from the cathode ray discharge tube experiment the characteristics of cathode rays (electrons) does not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube. Which concludes that electrons are the basic constituent of all the atoms

This is a Multiple Choice Questions as classified in NCERT Exemplar

ANS – Option (iv)

The probability density of electrons for 2s orbital decreases uniformly as distance from the nucleus increases. Electrons at the 1s orbital decreases as we move far from the nucleus, however in case of 2s the probability decreases initially then it increases with the distance and thereafter at a certain point it starts decreasing with the distance.

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Molecular mass of Ca₃ (PO₄)₂ = 310.18 g / mole 

Given mass of calcium 4 x 30= 120 g

Given mass of phosphorous =  31 x 2 =62 g

Given mass of oxygen = 16 x 8 = 128 g

Mass percent of Calcium = $\frac{120}{310.18\mathrm{}}$ x 100 = 38.71%

Mass percent of Phosphorous = $\frac{62}{310.18\mathrm{}}$  x 100 = 20%

Mass percent of Oxygen = $\frac{128}{310.18\mathrm{}}$ x 100 = 41.29 %

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans: (ii) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4s²

As per the Hund's rule the half-filled and fully filled orbital leads to the extra stability due to the symmetry thus fully filled 3d and half-filled 4s is preferred.

This is a Multiple Choice Questions as classified in NCERT Exemplar

 Ans: Option (iii)

Electrons move in a circular path of fixed energy called orbits .

As per Rutherford's α-particle scattering experiment the nucleus is surrounded by electrons that move around the nucleus with a very high-speed in circular paths called orbits. It does not mention the energy or stability of the electrons revolving around the nucleus. 

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SI unit of the mole is mol. The amount of a substance that contains as many particles or entities as there are atoms in exactly

12 g (0.012 kg) of the C-12  isotope is defined as a mole. One mole is defined as follows:

1 mole =  6.023 x 10²³

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On solving the above equation, the result is 5.4. All non-zeroes digits are significant. The significant figure is 2.

This is a Short Answer Type Questions as classified in NCERT Exemplar

Mass of 1 mole of C-12 = 12g

1 mole contains 6.022*10²³ atoms.

Thus, mass of 6.022*10²³ atoms=12g

 Mass of 1 atom of carbon =126.022*10²³ g
                                         =1.99*10⁻²³ g

Thus, mass of one atom of C-12 is 1.99*10⁻²³ g

This is a Short Answer Type Questions as classified in NCERT Exemplar
Ans: The energy of electrons is determined by the value of n in the hydrogen atom and by n + l in the multielectron atom. Thus for a given principal quantum number the electrons of different orbitals would have different energy.