An organic compound P with molecular formula C₉ H₁₈ O₁₂ decolorizes bromine water and also shows positive iodoform test. P on ozonolysis followed by treatment with H₂ O₂ gives Q and R. While compound Q shows positive iodoform test, compound R does not give positive iodoform test. Q and R on oxidation with pyridinium chlorochromate (PCC) followed by heating give S and T, respectively. Both S and T show positive iodoform test.

Complete copolymerization of 500 moles of Q and 500 moles of R gives one mole of a single acyclic copolymer U.

[Given, atomic mass: H =1, C = 12, O =16]

Question: Sum of number of oxygen atoms in S and T is _____.

The correct answer is 2.

Let us analyze the chemical reactions and step-by-step logic given in the problem:

1. Molecular Formula & Reactions of P:
Compound P has the molecular formula C₉H₁₈O₁₂ (or logically a monomer unit/structure related to the reactions).
P decolorizes bromine water, indicating the presence of a carbon-carbon double bond (C=C).
P gives a positive iodoform test, indicating a methyl ketone (CH₃-C(=O)-) or a methyl secondary alcohol (CH₃-CH(OH)-) group.

2. Ozonolysis of P:
Ozonolysis of P followed by oxidative workup with H₂O₂ yields two compounds, Q and R.
- Q gives a positive iodoform test.
- R does not give a positive iodoform test.

3. Oxidation of Q and R with PCC:
- Q on oxidation with pyridinium chlorochromate (PCC) followed by heating yields compound S.
- R on oxidation with PCC followed by heating yields compound T.
- Both S and T show a positive iodoform test.

4. Structure and Oxygen Content of S and T:
- Compound S is a small organic molecule formed by oxidation/decarboxylation that contains a methyl ketone group capable of showing a positive iodoform test and contains exactly 1 oxygen atom.
- Compound T is also an organic molecule formed by oxidation of R with PCC followed by heating, which produces a methyl ketone group that shows a positive iodoform test and also contains 1 oxygen atom.
- Specifically, S and T each contain 1 oxygen atom (such as acetone, CH₃COCH₃, which has 1 oxygen atom).

5. Calculation:
- Number of oxygen atoms in S = 1
- Number of oxygen atoms in T = 1

$\text{Sum of number of oxygen atoms in S and T}=1+1=2$

Thus, the sum of the number of oxygen atoms in S and T is 2.