The quantum theory was initially regarded as absurd, unnatural and ____ with…

Concept: In sentence-completion items, when several words or phrases are joined by ‘and’ in a list, they usually share the same tone and the same shade of meaning. The word that fills the blank must continue that shared tone, not contradict it.

Application: Here, ‘absurd’ and ‘unnatural’ are both negative, dismissive words describing how quantum theory looked when it was new — they say the theory seemed foolish and against the natural order of things. The joining word ‘and’ signals that the blank needs a third word carrying that same critical, negative flavour. ‘Incompatible’ (in conflict, unable to coexist) keeps that tone exactly: it says the theory clashed with common sense, matching ‘absurd’ and ‘unnatural’ perfectly.

Contrast with the other words:

• consanguineous — this word means ‘related by blood or descent’; it describes kinship between people, not how an idea relates to common sense, so it does not fit the sentence's meaning at all.

• discernible — this word means ‘able to be perceived or noticed’, describing whether something CAN be picked out by the senses or mind; it says nothing about clashing or conflicting with common sense, so it cannot continue the sentence's negative, critical thread.

• decipherable — this word means ‘able to be worked out or decoded’, describing whether something CAN be understood; like ‘discernible’, it describes comprehensibility, not opposition, so it does not carry the required sense of clashing with common sense.

So the word that keeps the same critical, dismissive tone as ‘absurd’ and ‘unnatural’ is the one that correctly completes the sentence.