Which of the following biomolecules acts as specific catalysts in biological reactions?

$A$ radioactive material decays by simultaneous emission of two particles with respective half-lives $1620 \, years$ and $810 \, years$. The time (in years) after which one-fourth of the material remains is:

The displacement equations of sound waves produced by two sources are given by $y_1 = 5 \sin(400 \pi t)$ and $y_2 = 8 \sin(408 \pi t)$, where $t$ is time in seconds. If the waves are produced simultaneously, the number of beats produced per minute is

Aluminium is extracted from alumina $(Al_2O_3)$ by electrolysis of a molten mixture of:

The point of intersection of the pair of lines represented by $x^2+xy+2y^2-3x+2y+4=0$ is

What is the decreasing order of reactivity amongst the following compounds towards aromatic electrophilic substitution?
$(i)$ Chlorobenzene
$(ii)$ Benzene
$(iii)$ Anilinium chloride
$(iv)$ Toluene