Which statements about mercury are correct?

Hint: Mercury is considered to be one of the unique metals in the periodic table. It is not like other common metals and does not show properties similar to them. Since mercury is a transition element it has variable valency and hence forms different types of compounds. Mercury forms amalgam with other metals except few of them.

Complete answer:
Mercury is an element with the symbol Hg , atomic number 80. The common name for mercury is quicksilver and was formerly called hydrargyrum which is its Latin name .
Mercury is a heavy, silvery d-block element that is liquid at standard conditions for temperature and pressure; the only other element that is liquid under these conditions is the halogen element bromine, although metals like caesium, gallium, and rubidium melt just above room temperature.
In amalgam formation the metal ion is reduced to original atom configuration and this metal atom is then solvated by mercury atom to form amalgam. So, Mercury has to solvate iron atoms by incorporating in the iron lattice .This is difficult as the iron lattice is very strong. This stability of the iron is due to its electronic configuration. Like iron, mercury cannot form amalgam with elements like platinum and cadmium as well.
Since Mercury ion exists in two forms i.e. +1 and +2 , mercury forms two sets of compounds, salts. However, the anhydrous form of mercury does not show variable valency.
Therefore, from the above explanation we can conclude that all the given options are correct.

Note:
Mercury is widely used in thermometers, barometers, manometers, float valves, relays switches. However, the toxicity of mercury has led to mercury thermometer and sphygmomanometers being phased out and replaced with alcohol which is not hazardous.