Which of the following has cross-links?

Match the following:

List-$I$	List-$II$
$A$. $(CH_2-C(Cl)=CH-CH_2)_n$	$I$. Cross-linked network
$B$. Nylon-$6,6$	$II$. Elastomer
$C$. $HDP$	$III$. Fibre
$D$. Melamine-formaldehyde	$IV$. Ziegler-Natta catalyst

The bond energy of $C=C$ and $C-C$ at $298 \ K$ are $590 \ kJ \ mol^{-1}$ and $331 \ kJ \ mol^{-1}$ respectively. The enthalpy of polymerisation per mole of ethylene is $..... \ kJ$.

Match List-$I$ with List-$II$.

List-$I$ (Chemicals)	List-$II$ (Use / Preparation / Constituent)
$(a)$ Alcoholic potassium hydroxide	$(i)$ Electrodes in batteries
$(b)$ $Pd / BaSO_4$	$(ii)$ Obtained by addition reaction
$(c)$ $BHC$ (Benzene hexachloride)	$(iii)$ Used for $\beta$-elimination reaction
$(d)$ Polyacetylene	$(iv)$ Lindlar's catalyst

Choose the most appropriate match.

An organic compound $P$ with molecular formula $C_{9}H_{18}O_{2}$ decolorizes bromine water and also shows a positive iodoform test. $P$ on ozonolysis followed by treatment with $H_{2}O_{2}$ gives $Q$ and $R$. While compound $Q$ shows a positive iodoform test,compound $R$ does not. $Q$ and $R$ on oxidation with pyridinium chlorochromate $(PCC)$ followed by heating give $S$ and $T$,respectively. Both $S$ and $T$ show a 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: $H=1, C=12, O=16$ ]
$(1)$ Sum of the number of oxygen atoms in $S$ and $T$ is. . . . . .
$(2)$ The molecular weight of $U$ is
Give the answer for questions $(1)$ and $(2)$.

Which of the following is the correct formula for the given polymer?