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121.
Based on the equation : $$\Delta E = - 2.0 \times {10^{ - 18}}J\left( {\frac{1}{{n_2^2}} - \frac{1}{{n_1^2}}} \right)$$ the wavelength of the light that must be absorbed to excite hydrogen electron from level $$n = 1$$ to level $$n = 2$$ will be : $$\left( {h = 6.625 \times {{10}^{ - 34}}Js,\,C = 3 \times {{10}^8}m{s^{ - 1}}} \right)$$
122.
The value of Planck’s constant is $$6.63 \times {10^{ - 34}}Js.$$ The speed of light is $$3 \times {10^{17}}nm\,{s^{ - 1}}.$$ Which value is closest to the wavelength in nanometer of a quantum of light with frequency $$6 \times {10^{15}}{s^{ - 1}}?$$
123.
According to Bohr’s theory the energy required for the transition of $$H$$-$$atom$$ from $$n = 6$$ to $$n = 8$$ state is
A
equal to the energy required for the transition from $$n = 5$$ to $$n = 6$$ state
B
larger than in (A)
C
less than in (A)
D
equal to the energy required for the transition from $$n = 7$$ to $$n = 9$$ state.
Answer :
less than in (A)
The difference between the energy of adjacent energy levels decreases on moving away from nucleus.
124.
In a hydrogen atom, if energy of an electron in ground state is $$13.6.\,ev,$$ then that in the 2nd excited state is
A
$$1.51\,eV$$
B
$$3.4\,eV$$
C
$$6.04\,eV$$
D
$$13.6\,eV$$
Answer :
$$1.51\,eV$$
2nd excited state will be the 3rd energy level.
$${E_n} = \frac{{13.6}}{{{n^2}}}eV\,\,{\text{or}}\,\,E = \frac{{13.6}}{9}eV$$ $$ = 1.51\,eV.$$
125.
The correct set of four quantum numbers for the valence electron of rubidium atom $$\left( {{\text{at}}{\text{.}}\,{\text{no}}{\text{.}}\, = 37} \right)$$ is
A
$$5,1,1, + \frac{1}{2}$$
B
$$6,0,0, + \frac{1}{2}$$
C
$$5,0,0, + \frac{1}{2}$$
D
$$5,1,0, + \frac{1}{2}$$
Answer :
$$5,0,0, + \frac{1}{2}$$
$$\eqalign{
& _{37}Rb = {\,_{36}}\left[ {Kr} \right]5{s^1} \cr
& {\text{Its valence electron is}}\,\,5{s^1}. \cr
& n = 5 \cr
& l = 0\,\,\,\left( {{\text{For }}s{\text{ - orbital}}} \right) \cr
& m = 0\,\,\left( {{\text{As }}m = - l\,{\text{to}}\, + l} \right) \cr
& s = + \frac{1}{2} \cr} $$
126.
Which of the following is the energy of a possible excited state of hydrogen ?
127.
The energy required to break one mole of $$Cl - Cl$$ bonds in $$C{l_2}$$ is $$242\,kJ\,mo{l^{ - 1}}.$$ The longest wavelength of light capable of breaking a single $$Cl - Cl$$ bond is
( $${c = 3 \times {{10}^8}m{s^{ - 1}}}$$ and $${{N_A} = 6.02 \times {{10}^{23}}mo{l^{ - 1}}}$$ )
128.
The number of radial nodes for $$3p$$ orbital is ___________.
A
3
B
4
C
2
D
1
Answer :
1
No. of radial nodes $$ = n - l - 1$$
For $$3p$$ orbital, $$n = 3,l = 1$$
∴ No. of radial nodes for $$3p$$ orbital
$$\eqalign{
& = 3 - 1 - 1 \cr
& = 3 - 2 \cr
& = 1 \cr} $$
129.
In Bohr series of lines of hydrogen spectrum, the third line from the red end corresponds to which one of the following inter-orbit jumps of the electron for Bohr orbits in an atom of hydrogen
A
$$5 \to 2$$
B
$$4 \to 1$$
C
$$2 \to 5$$
D
$$3 \to 2$$
Answer :
$$5 \to 2$$
The lines falling in the visible region comprise Balmer series. Hence the third line from red would be $${n_1} = 2,\,\,{n_2} = 5$$ i.e. $$5 \to 2.$$
130.
The energies $${E_1}$$ and $${E_2}$$ of two radiations are $$25\,eV$$ and $$50\,eV$$ respectively. The relation between their wavelengths, i.e. $${\lambda _1}$$ and $${\lambda _2}$$ will be