When we heat the mixture of

CH₃CHO and CD₃CDO, we get

CH₃CHO → CH₄ + CO

CD₃CDO → CD₄ + CO

but radical mechanism indicates that we should obtain

Concept:

1. Thermal Decomposition of Aldehydes:- The process involves breaking the C-H bonds in the aldehyde molecule. - Involves radical intermediates leading to the formation of methane (or its isotoped variants) and carbon monoxide.
2. Isotopic Labeling:- CD3CDO is an isotopically labeled compound where deuterium (D) replaces hydrogen (H). - The radicals involved in the mechanism determine the distribution of hydrogen and deuterium in the products.

Explanation:

When we heat the mixture of CH3CHO (acetaldehyde) and CD3CDO (fully deuterated acetaldehyde), the expected reactions based on a simple interpretation are:

CH₃CHO → CH₄ + CO

CD₃CDO → CD₄ + CO

However, considering a radical mechanism, where intermediates can mix and exchange hydrogens and deuteriums, we have:

1. The radicals can recombine in various ways, leading to mixed isotopic products.
2. For instance, H and CD3, or CH3 and D, can recombine leading to methane with mixed isotopes.

This suggests the formation of partially deuterated methanes such as CH3D.

Conclusion:

The correct answer is CH₃D.