Each category of taxonomic hierarchy is referred to as a unit of . . . . . . .

For the parabola $y^2+6y-2x+5=0$:
$(I)$ The vertex is $(-2,-3)$
$(II)$ The directrix is $y+3=0$
Which of the following is correct?

The slope of the tangent to the curve $x=t^{2}+3t-8, y=2t^{2}-2t-5$ at the point $(2,-1)$ is

Which property of hydrogen distinguishes it from alkali metals?

The eccentricity of the ellipse $\frac{x^2}{16} + \frac{y^2}{9} = 1$ is

The maximum potential energy due to electrostatic repulsion between two hydrogen nuclei is nearly (radius of the nucleus $= 1.1 \text{ fermi}$). $\left[\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \text{ Nm}^2 \text{C}^{-2}\right]$ (in $MeV$)