Question
Last element of group-$IV$ is found to be
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Figure $\xrightarrow[{0\, - \,5\,\,{\,^o}C}]{{HN{O_2}}}$ $P$ $\xrightarrow{{HB{F_4}}}Q$ $\xrightarrow[{Cu,\,\,\Delta }]{{NaN{O_2}}}R$

$(A)$ $2 CO ( g )+ O _2( g ) \rightarrow 2 CO _2( g ) \quad \Delta H _1^\theta=- x\,kJ\,mol { }^{-1}$
$(B)$ $C$ (graphite) $+ O _2$ (g) $\rightarrow CO _2$ (g) $\Delta H _2^\theta=- y\,kJ\,mol -1$ The $\Delta H ^\theta$ for the reaction $......$.$C ($ graphite $)+\frac{1}{2} O _2( g ) \rightarrow CO ( g )$ is