Which of the statements given below is incorrect?

1. \(\mathrm{C l_{2} O_{7  }}\)${}_{}$is an anhydride of perchloric acid
2. \(\mathrm{O_{3}}\)${\mathrm{}}_{}$ molecule is bent
3. ONF is isoelectronic with \(\mathrm{N O_{2}^{-}}\)${}_{}^{}$ 
4. \(\mathrm{O F_{2}}\) is an oxide of fluorine

The variation of the boiling point of the hydrogen halides is in the order HF > HI > HBr > HCl. 
The higher boiling point of hydrogen fluoride is explained as:

The given sequence among the following arrangements that is not strictly according to the property indicated against it.  

Which of the following compounds has the lowest melting point?

1.  ${\mathrm{CaBr}}_2$

2.  ${\mathrm{Cal}}_2$

3.  ${\mathrm{CaF}}_2$

4.  ${\mathrm{CaCl}}_2$

Among the following which is the strongest oxidising agent?

1. $F_2$

2. $B{r}_2$

3. $l_2$

4. $C{l}_2$