Which one of the following is not a functional unit of an ecosystem?

The work function of a metal is $2 \text{ eV}$. If a radiation of wavelength $3000 \text{ Å}$ is incident on it,the maximum kinetic energy of the emitted photoelectrons is (Planck's constant $h = 6.6 \times 10^{-34} \text{ J s}$; velocity of light $c = 3 \times 10^8 \text{ m/s}$; $1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}$)

The normal at a point on the parabola $y^2=4x$ passes through $(5,0)$. If two more normals to this parabola also pass through $(5,0)$,then the centroid of the triangle formed by the feet of these three normals is

The current $i$ in the circuit will be:

$\operatorname{cosec} 15^{\circ} + \sec 15^{\circ}$ is equal to :

$A$ gas cylinder can withstand a pressure of $15 \, atm$. The pressure in the cylinder is $12 \, atm$ at $27 \, ^oC$. Up to what temperature in $^oC$ will the cylinder not burst?