What is the role of limestone during the extraction of iron from haematite ore?

$A$ marine cartilaginous fish that can produce electric current is

When the temperature of a black body increases,it is observed that the wavelength corresponding to maximum energy changes from $0.26 \mu m$ to $0.13 \mu m$. The ratio of the emissive powers of the body at the respective temperatures is

$P, Q$ and $R$ are long parallel straight wires in air, carrying currents as shown. The direction of the resultant force on $R$ is:

Which of the following is a chlorinated hydrocarbon?

What does the following figure represent?