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:

Which one of the following statements is not correct?

$A$ metal ion involved in stomatal regulation is

The number of common tangents to the two circles $x^2+y^2-8x+2y=0$ and $x^2+y^2-2x-16y+25=0$ is:

Consider the following statements about manganate and permanganate ions. Identify the correct statements:
$(A)$ The geometry of both manganate and permanganate ions is tetrahedral.
$(B)$ The oxidation states of $Mn$ in manganate and permanganate are $+7$ and $+6$, respectively.
$(C)$ Oxidation of $Mn(II)$ salt by peroxodisulphate gives manganate ion as the final product.
$(D)$ Manganate ion is paramagnetic and permanganate ion is diamagnetic.
$(E)$ Acidified permanganate ion reduces oxalate, nitrite and iodide ions.
Choose the correct answer from the options given below:

Two small drops of mercury,each of radius $R$,coalesce to form a single large drop. The ratio of the total surface energies before and after the change is