Ncert Solutions Chemistry Class 11th

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

(Natural abundance of 1H x molar mass ) + (Natural abundance of ²H x molar mass of 2H)

Natural abundance of  ¹H = 99.985

Natural abundance of ²H = 0.015

Average atomic mass = $\frac{99.985+0.030}{100\mathrm{}}$

$\frac{100.015}{100\mathrm{}}$ = 1.00015u

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans:  Option (iv)

sum of the number of protons and neutrons is same but the number of protons is different

Isobars are the atoms which have same mass number (sum of number of neutrons and protons) but different atomic number (i.e. different proton number)

For example, ₁₄⁶C and ₁₄⁷N.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans:  Option (i)

Overall neutrality of atom.

According to the J.J Thomson model the positive charge is uniformly distributed and the electrons are embedded into it in such a manner as to give the most stable electrostatic arrangement just as watermelon of positive charge with plums or seeds (electrons) embedded into it. Thus this model is able to explain the overall neutrality of the atom

This is a Multiple Choice Questions as classified in NCERT Exemplar

Ans:  Option (ii)

The mass of an electron is equal to the mass of a neutron.

The neutron is heavier than the electron as

Mass of the neutron = 1.67 x 10^-27 kg

Mass of the electron = 9.11 x 10^-31kg

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.

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

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.