$\bullet$ Diadelphous condition is a condition of arrangement of filaments and stamen in a flower, e.g. Pea. In this condition, filaments of nine different stamens are connected into one unit and the tenth posterior stamen remains out of the bundle as a stand part. The androecium of pea flower is diadelphous because the filaments of the anther are united in two bundles. In the case of pea, out of ten, nine stamens form a staminal tube while one is free. Thus, the correct answer is 'Pea' which exhibit diadelphous condition

$\bullet$ China rose has monoadelphous stamens while, Citrus has polyadelhphous stamens. Monoadelphous stamens are grouped in single bundle whereas polyadelphous stamens occur in more than two bundles.