NEET Sample Paper NEET Sample Test Paper-9

  • question_answer The longest wavelength that a single ionized helium atom in its ground state will absorb is:

    A)  \[912\overset{o}{\mathop{A}}\,\]                

    B)  \[304\overset{o}{\mathop{A}}\,\]

    C)  \[229\overset{o}{\mathop{A}}\,\]                

    D)  \[687\overset{o}{\mathop{A}}\,\]

    Correct Answer: B

    Solution :

    As,       \[\Delta {{\varepsilon }_{12}}=\frac{hc}{{{h}_{\max }}}\] For \[He,\]       \[z=2,\] and for longest wavelength             \[{{n}_{1}}=1\] and  \[{{n}_{2}}=2\] Now,    \[\frac{1}{\lambda }=Z_{R}^{2}\,\,\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\]                 \[=4\times 1.097\times {{10}^{7}}\left( 1-\frac{1}{4} \right)\]                 \[=4\times 1.097\times {{10}^{7}}\times \frac{3}{4}\]                 \[\frac{1}{\lambda }=3.29\times {{10}^{7}}/m\] So,       \[\lambda =\frac{1}{3.29\times {{10}^{7}}}\]                 \[\lambda =0.3039\times {{10}^{-7}}m=304\overset{o}{\mathop{A}}\,\]

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