Which of the following species is not stable?

A small hole of area of cross-section 2 mm² present near the bottom of a fully filled open tank of height 2 m. Taking g = 10 m/s², the rate of flow of water through the open hole would be nearly :

Ionized hydrogen atoms and $$\alpha $$-particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r_H : r_{$$\alpha $$} will be :

When a block of mass M is suspended by a long wire of length L, the length of the wire becomes (L + $$l$$). The elastic potential energy stored in the extended wire is :