Which of the following crops were introduced into India from the New World?

Which of the following is known as the $Christmas$ tree?

The heat evolved for the rise of water when one end of the capillary tube of radius $r$ is immersed vertically into water is (Assume surface tension $= T$ and density of water to be $\rho$)

In a triangle,if $r_1 = 2r_2 = 3r_3$,then $\frac{a}{b} + \frac{b}{c} + \frac{c}{a}$ is equal to

Which one of the following frequencies of radiation (in $Hz$) has a wavelength of $600 \ nm$?

Name the gas that can readily decolourise acidified $KMnO_4$ solution.