Which of the following elements has the highest melting point?

The ratio of the de-Broglie wavelength of an $\alpha$-particle to that of a proton,when both are subjected to the same magnetic field such that the radii of their paths are equal,assuming the magnetic field induction vector $\overrightarrow{B}$ is perpendicular to the velocity vectors of both particles,is:

The wavelength of the first line in the Balmer series in the hydrogen spectrum is $\lambda$. What is the wavelength of the second line?

$\int \frac{dx}{\sqrt{x-x^2}}$ is equal to

The hand of a man,the wing of a bat,and the flipper of a seal represent:

In any $\triangle ABC$,$a(b \cos C - c \cos B)$ equals