The word 'geological' means 'relating to the study of the earth's physical structure.' Consider the phrase 'geological map of the city'.
From the options, 'physiological' means 'relating to a branch of biology that deals with the functioning of living beings'. Consider: 'physiological research on the causes of asthma'. It means the opposite of the given word; geology relates to the earth's physical structure whereas physiological relates to the physical functioning of a living being. Hence option D is the correct option.
'Astral' relates to or resembles to stars, it is not connected to the given word.
Similarly, 'solar' relates to the sun and 'galactic' relates to galaxies; these words are completely unrelated to 'geology'. Hence they cannot be called its opposites and options A, B and C are incorrect.