An unripe green fruit changes colour when it ripens. The reason is

Correct option is C

The correct answer is chloroplast changes to chromoplast.
Chromoplast are coloured plastids containing pigments other than chlorophylls. Chromoplasts contain fat soluble carotenoid pigments and are yellow, orange or red in colour. They are formed either from leucoplast or chloroplasts. Change of colour from green to red during ripening of many fruits (tomatoes, chillies) is due to transformation of chloroplast to chromoplasts. Orange colour of carrot is due to the presence of chromoplasts. The latter also provides colour to many flowers and fruits.