CBSE JEE Main & Advanced Chemistry: Atomic Structure Important Questions & Complete Chapter Notes

Correct Answer: (d)

Explanation: According to Dalton's atomic theory, symbol of hydrogen is  and for oxygen  and for sulphur  and for nitrogen  . In the given option  this symbol represent the water molecule.

Correct Answer: (a)

Explanation: For a hydrogen atom, the energy of an electron in the $n$th stationary state is $ E_n=\frac{-2.18\times10^{-18}}{n^2}\ \text{J} $ For $n=2$, $ E_2=\frac{-2.18\times10^{-18}}{2^2} =\frac{-2.18\times10^{-18}}{4} =-5.45\times10^{-19}\ \text{J} $ The negative sign shows that the electron is bound to the nucleus. $ \boxed{-5.45\times10^{-19}\ \text{J}} $ Hence, **Option A** is correct.

Correct Answer: (c)

Explanation: Energy of photon $ E=\frac{1240}{\lambda(\mathrm{in} \mathrm{~nm})}=\frac{1240}{310}=4.0 \mathrm{eV} $ Given work functions $M_1=4.8 \mathrm{eV}$ $M_2=4.3 \mathrm{eV}$ $M_3=4.75 \mathrm{eV}$ $\mathrm{M}_4=3.75 \mathrm{eV}$ Only metals with $\phi \leq 4.0 \mathrm{eV}$ will emit electrons. $M_1, M_2$ and $M_3$ have work functions greater than 4.0 eV thus, do not show no photoelectric effect.

Correct Answer: (d)

Explanation: Only the group I elements of periodic table exhibit the photoelectric effect because they are highly electropositive metals and have low ionisation enthalpy. Hence, only Cs shows photoelectric effect among the given options.

Correct Answer: (d)

Explanation: Bohr atomic model could not explain the ability of atoms to form molecules by chemical bonds.