Which one of the following is not correct?

$A$ parallel plate capacitor of capacity $C_0$ is charged to a potential $V_0$. $(i)$ The energy stored in the capacitor when the battery is disconnected and the plate separation is doubled is $E_1$. (ii) The energy stored in the capacitor when the charging battery is kept connected and the separation between the capacitor plates is doubled is $E_2$. Then,the value of $E_1 / E_2$ is:

The ratio of diameters of two wires of the same material is $n : 1$. The length of the wires is $4\, m$ each. On applying the same load,the increase in length of the thin wire will be

If $\tan A + \cot A = 4,$ then $\tan^4 A + \cot^4 A$ is equal to

Two resistances of $400 \ \Omega$ and $800 \ \Omega$ are connected in series with a $6 \ V$ battery of negligible internal resistance. $A$ voltmeter of resistance $10,000 \ \Omega$ is used to measure the potential difference across the $400 \ \Omega$ resistor. The error in the measurement of the potential difference in volts is approximately:

Methanogens belong to: