For an organic compound that does not react with both hydrogen cyanide (HCN) and hydroxylamine (NH₂OH).

Hydrogen cyanide undergoes nucleophilic addition reactions with compounds containing a carbonyl group ($C=O$), specifically aldehydes and ketones, to form cyanohydrins.

• Alkanones (ketones) have a $C=O$ group and react with HCN.
• Alkanals (aldehydes) have a $C=O$ group and react with HCN.
• Alkanoic acids have a $C=O$ group as part of a carboxyl group ($COOH$), but their carbonyl carbon is less reactive towards nucleophilic addition compared to aldehydes and ketones, so they generally do not form cyanohydrins.
• Alkenes have a carbon-carbon double bond ($C=C$) but no $C=O$ group, so they do not react with HCN in this manner.

Hydroxylamine reacts with compounds containing a carbonyl group ($C=O$), specifically aldehydes and ketones, to form oximes. This is a nucleophilic addition-elimination reaction.

• Alkanones (ketones) have a $C=O$ group and react with $NH_2OH$.
• Alkanals (aldehydes) have a $C=O$ group and react with $NH_2OH$.
• Alkanoic acids do not typically react with hydroxylamine to form oximes at the carboxyl carbon.
• Alkenes have no $C=O$ group, so they do not react with $NH_2OH$ to form oximes.

Based on this analysis:

• Alkanones and Alkanals react with both HCN and $NH_2OH$.
• Alkanoic acids generally do not undergo these specific reactions.
• Alkenes do not have a carbonyl group ($C=O$) and therefore do not undergo these characteristic reactions with either HCN or $NH_2OH$.

Thus, an alkene is the compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine.

The correct option is B.