acidic nature

2. if the angle between the lone pair ,the central atom and bond pair is increased ,it follows that the actual bond angle between the atoms must decrease

The more oxygens(double bonded), the more scope for resonance of negative charge on conjugate base of the acid, and hence stronger the acid.
Besides, the electronegativity of the oxygens makes it easier for the proton to be dislodged by a base.

yes,pritish gav d correct explanation of d 1st 1....coz d conjugate base becomes more stable

for d second 1,lone pair-lone pair repulsion> lone pair-bond pair repulsion> bond pair-bond pair repulsion
....so as d angle between lone pairs increase,d angle between lone pair-bond pair n bond pair-bond pair decrease