The $pH$ value of which one of the following is not equal to $1$?

Electrons ejected from the surface of a metal,when light of certain frequency is incident on it,are stopped fully by a retarding potential of $3 \ V$. Photoelectric effect in this metallic surface begins at a frequency $6 \times 10^{14} \ s^{-1}$. The frequency of the incident light in $s^{-1}$ is : [Planck's constant $= 6.4 \times 10^{-34} \ J \ s$,charge on the electron $= 1.6 \times 10^{-19} \ C$]

In order to eliminate the first degree terms from the equation $2x^2 + 4xy + 5y^2 - 4x - 22y + 7 = 0$,the point to which the origin is to be shifted is:

$A$ piece of copper and another of germanium are cooled from room temperature to $80\,K$. Which of the following is a correct statement?

Consider the following two statements,$A$ and $B$ and identify the correct answer given below:
$A$. Nuclear density is same for all nuclei.
$B$. Radius of the nucleus $R$ and its mass number $A$ are related as $\sqrt{A} \propto R^{1 / 6}$.

Two circular coils $1$ and $2$ are made from the same wire,but the radius of the $1^{st}$ coil is twice that of the $2^{nd}$ coil. What is the ratio of potential difference in volts that should be applied across them so that the magnetic field at their centres is the same?