The successive ionisation energy values for an element ' $X$ ' are given below :

(i) 1st ionisation energy $=410 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(ii) 2nd ionisation energy $=820 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(iii) 3rd ionisation energy $=1100 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(iv) 4th ionisation energy $=1500 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(v) 5th ionisation energy $=3200 \mathrm{~kJ} \mathrm{~mol}^{-1}$

$$ \text { Match the following : } $$

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">BF</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">BF</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">ClF</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">ClF</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">NH</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">NH</mi>

</mrow>

<mn>3</mn>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">NH</mi>

</mrow>

<mn>4</mn>

<mrow data-mjx-texclass="ORD">

  <mo>+</mo>

</mrow>

<mrow data-mjx-texclass="ORD">

  <mi data-mjx-auto-op="false">NH</mi>

</mrow>

<mn>4</mn>

<mrow data-mjx-texclass="ORD">

  <mo>+</mo>

</mrow>

$$ \text { The correct match is } $$

Which of the following molecules does not exist according to molecular orbital theory?

Root mean square ( rms ) speed of $\mathrm{O}_2$ is $500 \mathrm{~m} / \mathrm{s}$ at a constant temperature. Calculate the rms speed and the average kinetic energy of $\mathrm{H}_2$ at the same temperature. (Consider, $R=8.33 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$ )