Which of the following has the minimum bond length?

1.  ${\mathrm{O}}_2^{-}$

2.  ${\mathrm{O}}_2^{2-}$

3.  ${\mathrm{O}}_2$

4.  ${\mathrm{O}}_2^{+}$

Acidified K₂Cr₂O₇ solution turns green when Na₂SO₃ is added to it. This is due to the formation of:

1.  ${\mathrm{CrO}}_4^{2-}$

2.  ${\mathrm{Cr}}_2{\left({\mathrm{SO}}_3\right)}_3$

3.  ${\mathrm{CrSO}}_4$

4.  ${\mathrm{Cr}}_2{\left({\mathrm{SO}}_4\right)}_3$

Which one of the following statements is not true?

Find the correct sequence of filling of electrons for an atom having principal quantum number (n) equal to 6.

1. $\mathrm{ns}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-1\right)$ $\mathrm{d}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-2\right)$ $\mathrm{f}$ $\stackrel{}{\to }$ $\mathrm{np}$

2. $\mathrm{ns}$ $-$ $\left(\mathrm{n}-2\right)$ $\mathrm{f}$ $\stackrel{}{\to }$ $\mathrm{np}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-1\right)$ $\mathrm{d}$

3. $\mathrm{ns}$ $-$ $\mathrm{np}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-1\right)\mathrm{d}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-2\right)$ $\mathrm{f}$

4. $\mathrm{ns}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-2\right)$ $\mathrm{f}$ $\stackrel{}{\to }$ $\left(\mathrm{n}-1\right)$ $\mathrm{d}$ $\stackrel{}{\to }$ $\mathrm{np}$

 An active ingredient in bleaching powder that aids in the bleaching action is:

1.  $\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2$

2.  ${\mathrm{CaO}}_2\mathrm{Cl}$

3.  ${\mathrm{CaCl}}_2$

4.  ${\mathrm{CaOCl}}_2$