Which of the following metals releases hydrogen gas upon reaction with cold dilute $HNO_3$?

$A$ particle of mass $10\, g$ is kept on the surface of a uniform sphere of mass $100\, kg$ and radius $10\, cm$. Find the work to be done against the gravitational force between them to take the particle far away from the sphere (you may take $G = 6.67 \times 10^{-11}\, N m^2/kg^2$).

The line passing through $\left(-1, \frac{\pi}{2}\right)$ and perpendicular to $\sqrt{3} \sin \theta + 2 \cos \theta = \frac{4}{r}$ is :

Three rods each of length $L$ and mass $M$ are placed along $X$,$Y$,and $Z$-axes such that one end of each rod is at the origin. The moment of inertia of this system about the $Z$-axis is:

If a charged particle moves unaccelerated through a region containing both electric and magnetic fields,which of the following must be true?

If the axes are rotated through an angle $\alpha$,then the number of values of $\alpha$ such that the transformed equation of $x^2+y^2+2x+2y-5=0$ contains no linear terms is