When stamens are united into one bundle, what is the term used for this arrangement?

Monoadelphous

The correct answer is Option (3) -Monoadelphous

Androecium is composed of stamens. Each stamen which represents the male reproductive organ consists of a stalk or a filament and an anther.

Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in pollen-sacs.

A sterile stamen is called staminode. Stamens of flower may be united with other members such as petals or among themselves.

When stamens are attached to the petals, they are epipetalous as in brinjal, or epiphyllous when attached to the perianth as in the flowers of lily.

The stamens in a flower may either remain free (polyandrous) or may be united in varying degrees.

The stamens may be united into one bunch or one bundle (monoadelphous) as in china rose, or two bundles (diadelphous) as in pea, or into more than two bundles (polyadelphous) as in citrus. There may be a variation in the length of filaments within a flower, as in Salvia and mustard.