Two sigma bonds are present in

All oxo acids of Chlorine are monobasic….contain one O-H group/molecule ;

All the pi bonds in these acids or their oxanions are $\mathrm{d\pi }-\mathrm{p\pi }$ bonds ;

In all oxo acids of Chlorine the hybridization of Chlorine atom is sp³ ;

Cl-O bond  order….${\mathrm{ClO}}^{-} \left(1\right)<{\mathrm{ClO}}_2^{-}\left(1.5\right) <{\mathrm{ClO}}_2^{-} \left(1.66\right)<{\mathrm{ClO}}_4^{-}\left(1.75\right) ;$

No resonance in Hypochlorite ion, two resonance structures in Chlorite ion, three resonance structures in Chlorate ion, four resonance structures in Perchlorate ion ;

Cl-O bond length….${\mathrm{ClO}}^{-}>{\mathrm{ClO}}_2^{-}>{\mathrm{ClO}}_3^{-}>{\mathrm{ClO}}_4^{-} ;$

Bond angle….${\mathrm{ClO}}^{-}$-no bond angle …. diatomic species; ${\mathrm{ClO}}_3^{-}$- 107⁰ (3 bp+ 1 lp ); ${\mathrm{ClO}}_4^{-}$- 109.5⁰(4 bp); In ${\mathrm{ClO}}_2^{-}$ - 111⁰( 2 bp + 2 lp )….bp-bp repulsions dominate lp-lp repulsions ;

Acidic strength, oxidizing power, bleaching power…..$\mathrm{HClO}>{\mathrm{HClO}}_2>{\mathrm{HClO}}_3>{\mathrm{HClO}}_3 ;$

Basic strength…….${\mathrm{ClO}}^{-}>{\mathrm{ClO}}_2^{-}>{\mathrm{ClO}}_3^{-}>{\mathrm{ClO}}_4^{-} ;$

${\mathrm{ClO}}^{-}$ does not exhibit resonance ; ${\mathrm{ClO}}_4^{-}$ cannot undergo disproportionation…'Cl' is in its highest O.S ;

Stability….$\mathrm{HClO}<{\mathrm{HClO}}_2<{\mathrm{HClO}}_3<{\mathrm{HClO}}_4;$

Note : While counting the sigma bonds in these acids never forget to count a sigma bond between O-H bond ; 

Number of bond pairs around central atom = 3
Number of bond pairs around central atom according to VSPER theory =2
Number of lone pairs around central atom = 2
Orientation of electron pairs around central atom = Tetrahedral(sp³)
Shape of ${\mathrm{ClO}}_2^{-}$= Angular
Cl–O bond order = 3/2 = 1.5
It has two resonance structures.