Class 11th

(i) One mole of methane (CH₄) has = 6.022 * 10²³ molecules
     No. of electrons present in one molecule of CH₄ = 6 + (4 x 1) = 10
     No. of electrons present in 6.022 * 10²³ molecules of CH₄ = 6.022 * 10²³ * 10
     = 6.022 * 10²⁴ electrons

(ii)  (a) Calculation of total number of carbon atoms
            Gram atomic mass of carbon (C-14) = 14 g = 14 * 10³ mg
            14 g or 14 * 10³ mg of carbon (C-14) has 6.022 * 10²³ atoms

            No of neutrons on 1 atom of (C-14) = 14-6= 8

            ⇒ No. of neutrons in 14g of (C-14) = 6.022* 10²³ *8

            So, 7 mg of carbon (C-14) has = (6.022 * 10²³ *8) / (14 x 10³ mg) x (7 mg) = 2.408 * 10²¹ neutrons

        (b) Calculation of total number and total mass of neutrons
              Mass of one neutron = 1.675 * 10^-27 kg
              Mass of 2.408 * 10²¹ neutrons = (1.675 x 10^-27 kg) * 2.408 * 10²¹
              = 4.033 * 10^-6 kg

(iii) (a) Calculation of total number of NH₃ molecules
            Gram molecular mass of ammonia (NH₃) = 17 g = 17 * 10³ mg
            17 * 10³ mg of NH₃ have molecules = 6.022 * 10²³

            34 mg of NH₃ have molecules = (6.022 * 10²³) / (17 x 10³) x 34 mg = 1.2044 x 10²⁰ molecules

       (b) Calculation of total number and mass of protons
            No. of protons present in one molecule of NH₃ = 7 + 3 = 10
            No. of protons present in 12.044 * 10²⁰ molecules of NH₃ = 12.044 * 10²⁰ * 10
            = 1.2044 * 10²² protons
            Mass of one proton = 1.67 * 10^-27 kg
            Mass of 1.2044 * 10²² protons = (1.67 * 10^-27 kg) * 1.2044 * 10²²
            = 2.01 * 10^-5 kg

Since, the mass and number of protons is independent of the temperature and pressure conditions. So, there will no change in the answer upon changing the temperature and pressure because only the number of protons and mass of protons are involved.