Which of the following is the composition of a virus?

Which of the following is a fossil Pteridophyte?

The time period of a vibration magnetometer is $T_0$. Its magnet is replaced by another magnet whose moment of inertia is $3$ times and magnetic moment is $1/3$ of the initial magnet. The new time period will be:

The mass defect for the nucleus of helium is $0.0303 \, a.m.u.$ What is the binding energy per nucleon for helium in $MeV$?

The maximum possible number of real roots of the equation $x^5 - 6x^2 - 4x + 5 = 0$ is

$A$ body of mass $m$ hangs at one end of a string of length $l$,the other end of which is fixed. It is given a horizontal velocity so that the string just reaches a position where it makes an angle of $60^o$ with the vertical. The tension in the string at the mean position is: