The Curie temperatures of cobalt and iron are $1400 \,K$ and $1000 \,K$ respectively. At $T=1600 \,K$, the ratio of the magnetic susceptibility of cobalt to that of iron is

The magnetic needle of a magnetic compass is made up of $\qquad$ .

To protect an instrument from an external magnetic field,it is completely surrounded by:

The relation $H \propto I$ and the susceptibility $\chi = \frac{I}{H}$ are not applicable for which of the following substances?

Which of the following statements are correct?
$(A)$ Electric monopoles do not exist whereas magnetic monopoles exist.
$(B)$ Magnetic field lines due to a solenoid at its ends and outside cannot be completely straight and confined.
$(C)$ Magnetic field lines are completely confined within a toroid.
$(D)$ Magnetic field lines inside a bar magnet are not parallel.
$(E)$ $\chi = -1$ is the condition for a perfect diamagnetic material,where $\chi$ is its magnetic susceptibility.
Choose the correct answer from the options given below:

Given below are two statements; one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ Electromagnets are made of soft iron.
Reason $R:$ Soft iron has high permeability and low retentivity.
In the light of the above statements,choose the most appropriate answer from the options given below.