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$12. What do you understand by the terms:(c) Electron affinity$

$Q11. (a) Hydrogen atom and \mathrm{He}^{+} are mono-electronic system but the size of \mathrm{He}^{+} is much smaller than \mathrm{H}^{+} why?$

$Q9. (a) Derive the following equations for hydrogen atom which are related to the(i) energy difference between two levels \mathrm{n}_{1} and \mathrm{n}_{2} .$

$(vii) In the ground state of an atom the electron is present(a) in the nucleus(b) in the second shell(c) nearest to the nucleus(d) farthest from the nucleus$

Q 19 Bohrs equation for the radius of nth orbit of electron in hydrogen atom is$\mathrm{r}_{\mathrm{n}}=\frac{\epsilon_{0} \mathrm{~h}^{2} \mathrm{n}^{2}}{\pi \mathrm{e}^{2} \mathrm{~m}}$(b) What is the distance travelled by the electron when it goes from n=2 to n=3 and n=9 ton =10 ?$\left[\varepsilon_{0}=8.85 \times 10^{-12} \mathrm{c}^{2} \mathrm{~J}^{-1} \mathrm{~m}^{-1} \mathrm{~h}=6.624 \times .10^{-34} \mathrm{js} \pi=3.14 \mathrm{~m}=9.108 \times 10^{-31} \mathrm{~kg} \mathrm{e}=1.602 \times 10^{-19} \mathrm{c}\right]$ while doing calculations take care of units of energy parameter.$\left[=\mathrm{kgm}^{2} \mathrm{~s}^{-2} \mathrm{c}=\mathrm{kg}^{1 / 2} \mathrm{~m}^{3 / 2} \mathrm{~s}^{-1}\right]$

$Q2. Fill in the blanks with suitable words.(i) \beta -particles are nothing but moving with a very high speed.(ii) The charge on one mole of electrons is coulombs.(iii) The mass of hydrogen atom is grams.(iv) The mass of one mole of electrons is(v) Energy is when electron jumps from higher to a lower orbit.(vi) The ionization energy of hydrogen atom can be calculated from model of atom.(vii) For d-subshell the azimuthal quantum number has value of(viii) The number of electrons in a given subshell is given by formula(ix) The electronic configuration of \mathrm{H}^{+} is$

$14. (a) The ionization potential of Lithium and potassium are 5.4 and 4.3 \mathrm{ev} . what do you predict for the I.P. of \mathrm{Na} .$