Which part of the tobacco plant is infected by $Meloidogyne$ $incognita$?

Which of the following statements is $NOT$ correct for potash alum?

An electron beam travels with a velocity of $1.6 \times 10^7 \ m/s$ perpendicularly to a magnetic field of intensity $0.1 \ T$. Calculate the radius of the path of the electron beam. (Given: $m_e = 9 \times 10^{-31} \ kg$,$e = 1.6 \times 10^{-19} \ C$)

One thousand small water drops of equal radii combine to form a big drop. The ratio of final surface energy to the total initial surface energy is

$A$ tension of $22 ~N$ is applied to a copper wire of cross-sectional area $0.02 ~cm^2$. The Young's modulus of copper is $1.1 \times 10^{11} ~N/m^2$ and the Poisson's ratio is $0.32$. The decrease in cross-sectional area will be:

Widal test is used for the diagnosis of