In a typical complete, bisexual and hypogynous flower the arrangement of floral whorls on the thalamus from the outermost to the innermost is:

In a typical complete, bisexual and hypogynous flower the arrangement of floral whorls on the thalamus from the outermost to the innermost is as follows:

Calyx – is the outermost part whorl of flower parts, consisting green leaf-like structures called sepals, which covers and protects the petals.

Corolla – is the second whorl of flower parts, which is composed of the flower’s petals.

Androecium - is the male reproductive part of the flower which is an essential whorl of the flower, it is made up of stamens.

Gynoecium - is the female reproductive part of the flower which is also an essential whorl of the flower, it is made up of pistils.

Therefore, the correct answer is (a).