What is the full form of $ARC$?

During electro-osmosis of $Fe(OH)_3$ sol,

Leaching of $Ag_2S$ is carried out by heating it with a dilute solution of

If $A(2,-1)$ and $B(6,5)$ are two points,the ratio in which the foot of the perpendicular from $P(4,1)$ to $AB$ divides $AB$ is:

$A$ slit of width $a$ is illuminated by red light of wavelength $6500 \,\, \mathring{A}$. The first minimum will fall at $\theta = 30^{\circ}$ if $a$ is equal to: