A colourless liquid 'A' contains H and O elements only. It decomposes slowly on exposure to light . It is stabilised any mixing urea to store in the presence of light.

Explanation

Since, a colourless liquid 'A' contains only hydrogen and oxygen and decoposes slowys on exposure to light but is stabilised by addition of urea, therefore ,liquid A may be hydrogen peroxide.
The structure of `H_(2)O_(2)` is

(a) `H_(2)O_(2)` structure in gas phase, dihedral angle is `111.5^(@)`.
(b) `H_(2)O_(2)` structure in solid phase at 110K , dihedral angle is `90.2^(@)`
(ii) `2H_(2)O_(2) underset ("Sunlight")overset(hv)to 2H_(2)O + O_(2)`