Updated (end bit)
1) Q5 of paper 23, O/N 2012.
According to the question:
” No oxygen atom is attached to any carbon atom which is involved in π bonding.”
This of course makes the later info about reaction of J and K with 2,4-DNPH and K with Tollens, simply impossible. I would have found it impossible to give any satisfactory answers for J and K, and probably left it blank – which would have been the WRONG thing to do!
The papers wording was wrong. It was suggested on the Teachers forum (by someone who actually writes CIE paper 2’s) that it should have read…
“no oxygen atom is attached to any carbon atom involved in pi bonding to another carbon atom”
The examiners report says:
” Many candidates realised compound H was an alcohol which contained a >C=C< bond and gave three correct structural isomers. Some candidates did not apply the data given and gave isomers with branched chains or an oxygen atom on a carbon atom involved in π bonding. Compound J was a ketone and compound K an aldehyde which some candidates got the wrong way round.”
Which is very strange because “Many candidates” who apparently did realise it, would have had to defy the first instruction!. No mention in the examiners report about the contradictory wording. Did they spot it? One wonders.
What to do in such situations? Well, really you HAVE to give some answer. That much is absolutely plain. Then you should assess the question and figure out the most clear or strongest info, then give an answer based on that.
For example, in this question the statements relating to 2,4-DNPH and Tollens are clearly telling you that there are carbonyls present and one of them is an aldehyde. The ” No oxygen atom is attached to any carbon atom which is involved in π bonding.” is the more complicated part is is likely to be the source of the conflict.
These occurrences are extremely rare so don’t start believing that the papers are full of errors. If you believe a question has an error, it’s most likely you are not understanding the question properly. You should always assume the question is right.