Which of the choices is an example of an element?
O CO
O Co
O C2H2O2
O CO2

Co(cobalt) is the answer

Explanation:

Cobalt is a chemical element with the symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

d: the voltage of the secondary coil is less than that of the primary coil.

im not suree sorry if wrong

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).