Question

Give reasonflowers that bloom at night have sweet fragrance

Answer 1

Day time flowering plants with colorful petals usually attract butterflies & other insects that are active during day time.

Night flowering plants usually attract moths & other nocturnal pollinators.

It makes sense why night blooming flowers are white, and mostly fragrant as well, because colorful pigments have no purpose to play at night. White flowers also reflect moonlight. Night blooming white flowers avoid the competition of pollinators with day blooming colorful flowers all together. It's nature's win-win situation for plants as well as pollinating creatures.

Answer 2

Flowers that bloom at night have sweet fragrance because on day flowers have bright colours to attract insect but at night they produce nectar and some are sweet smelling like Night jasmine to attract insects at night.