1. Which was the first superconducting material to be discovered ?

Mercury

2. What type of measurements were performed on it which suggested zero-resistance ?

For a fixed current, the voltage across a column of Hg was measured as a function of temperature and was found to become immeasurably small below about 4.18 K.

3. Which other special characteristics were superconductors found to have ?

Superconductors exhibit the Meissner effect wherein the flux is expelled from it in the superconducting state. They also exhibit the isotope effect wherein the depends on the isotopic mass.

4. Suggest a method of monitoring the current in a superconducting loop that does not involve interfering with the loop.

Since the current in the loop will generate a magnetic field, this can be monitored.

5. Which property characterises superconductivity along with zero electrical resistance ?

(a) Perfect Ferromagnetism

(b) Perfect Paramagnetism

(c) Perfect Diamagnetism

(d) The expulsion of any externally applied magnetic field.

(c). Since there is a critical field below which complete flux expulsion takes place, (d) is incorrect.