The correct option is
D Theory : Practical
The given word 'dulcet' means 'a sweet and soothing sound'.
'Raucous' means 'making or constituting a disturbingly harsh and loud noise'.
As you can see, the words are opposite in meaning. Hence, the relationship between them is that they are opposites, or antonyms.
Option A: 'Sweet' means 'pleasing in general'. 'Song' is 'a poem or composition that is uttered in musical tones'. 'Sweet' can be used as an adjective for 'song'. So the relation here is 'adjective-noun'.
Option B: 'Crazy' and 'insane' both mean 'mad'.
Option C: 'Palliative' means 'to care for the terminally ill and their families'. 'Exacerbating' means 'make a problem or negative feeling worse'.
The words do not express any relation between them.
These options do not express the same relation as that of the given pair of words. So options A, B and C are wrong.
Option D: 'Theory' is 'a system of ideas used to explain something'.
'Practical' means 'actually doing something to explain, rather than with theory and ideas'.
These words mean the opposite of one another and express the same relation as the given pair. Hence option D is correct.