Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

Along the $X$-axis,three charges $\frac{q}{2}, -q$ and $\frac{q}{2}$ are placed at $x=0, x=a$ and $x=2a$ respectively. The resultant electric potential at $x=a+r$ (if $a \ll r$) is: ($\varepsilon_0$ is the permittivity of free space)

The complete set of values of $x$ for which the function $f(x) = 2 \log_e(x-2) - x^2 + 4x + 1$ is increasing is:

$\int \frac{3^x dx}{\sqrt{9^x-1}}$ is equal to

$A$ long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the centre of the coil will be

$A$ patient who excretes a large quantity of sodium in urine has: