a. When `H_(2)O_(2)` is added to blood, rapid evolution of a gas occurs. Why ?
b. Hydrogen peroxide acts both as an oxidising and as a reducing agent in alkaline solution towards certain first row transition metal ions. Illustration both these properties of `H_(2)O_(2)` using chemical equations.

Explanation

`H_(2)O_(2)` is an oxidising agents in the basic medium.
`{:([cancel(2bar(e))+H_(2)O_(2)to2overset(Theta)(O)H]xx3),([5 overset(Theta)(O)H+H_(2)+underset(x=3)underset(x-3=0)(Cr(OH)_(3))tounderset(x=6)underset(x-8=-2)(CrO_(4)^(2-))+cancel(3bar(e))+5H_(2)O]xx2),(ulbar(4overset(Theta)(O)H+3H_(2)O_(2)+2Cr(OH)_(3) to 2Cr O_(4)^(2-)+8H_(2)O)):}`
b. `H_(2)O_(2)` is a reducing agent in basic medium.
`{:(H_(2)O_(2)+2overset(Theta)(O)HtoO_(2)+2H_(2)O+cancel(2bar(e))),([cancelbar(e)+[overset(3+)(F)e(CN)_(6)]^(3-)to[overset(2+)(F)e(CN)_(6)]^(-4)]xx2),(ulbar(2overset(Theta)(O)H+2[Fe^(3+)(CN)_(6)]^(3-)+H_(2)O_(2)+O_(2)to2H_(2)+2[Fe^(2+)(CN)_(6)]^(4-))):}`