Which is the largest flower?

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

Choose the correct statement$(s)$:
$(A)$ The position of the centre of mass of a system is dependent on the choice of the coordinate system.
$(B)$ Newton's second law of motion is applicable to the centre of mass of the system.
$(C)$ Internal forces cannot change the state of the centre of mass.
$(D)$ Internal forces can change the state of the centre of mass.

$A$ container is filled with water $(\mu = 1.33 \approx 4/3)$ up to a height of $33.25 \, cm$. $A$ concave mirror is placed $15 \, cm$ above the water level. The image of an object placed at the bottom is formed by the mirror at $25 \, cm$ below the water level. The focal length of the mirror is: (in $, cm$)

$A$ parallel beam of light of wavelength $6000 \, \mathring{A}$ is diffracted by a single slit of width $0.3 \, \text{mm}$. The angular position of the first minima of the diffracted light is:

$\sqrt{3} \operatorname{cosec} 20^{\circ} - \sec 20^{\circ}$ is equal to