In the following compounds,the order of acidity is:
$(I)$ Phenol
$(II)$ $p$-Cresol ($4$-methylphenol)
$(III)$ $m$-Nitrophenol
$(IV)$ $p$-Nitrophenol

$A$ body is sliding down a rough inclined plane. The coefficient of friction between the body and the plane is $0.5$. The ratio of the net force required for the body to slide down and the normal reaction on the body is $1:2$. Then the angle of the inclined plane is: (in $^{\circ}$)

Assertion : Cyclic pathway of photosynthesis first appeared in some eubacterial species.
Reason : Oxygen started accumulating in the atmosphere after the non-cyclic pathway of photosynthesis evolved.

Two identical piano wires have a fundamental frequency of $600 \text{ Hz}$ when kept under the same tension. What fractional increase in the tension of one wire will lead to the occurrence of $6 \text{ beats per second}$ when both wires vibrate simultaneously?

For the following cell reaction,$Ag|Ag^{+}|AgCl|Cl^{-}|Cl_2, Pt$
$\Delta G_f^{\circ}(AgCl) = -109 \ kJ / mol$
$\Delta G_f^{\circ}(Cl^{-}) = -129 \ kJ / mol$
$\Delta G_f^{\circ}(Ag^{+}) = 78 \ kJ / mol$
The $E^{\circ}$ of the cell is:

$C_6H_6 + 3O_3$ $\longrightarrow X \stackrel{Zn / H_2O}{}$ ${\longrightarrow} Y$; $X$ and $Y$ are respectively