Mercury have the lowest melting point among metals.

A metallic bond is characterized by free electrons and generally forms a specific geometric pattern of compact arrangement of atoms. All metals (except mercury) thus exist in a solid state at room temperature and have a specific crystal structure. Mercury belongs to the zinc group of elements in the periodic table, which comprises zinc, cadmium and mercury. They all have completely filled-up atomic orbitals. It becomes difficult to knock out these electron(s) from their orbitals and form metallic bonds. Therefore, they are soft (low melting point) and do not show multiple valence states unlike other transitional or rare earth metals. In mercury, the binding energy of outer electrons (towards nucleus) is highest and no electron is available to participate in metallic bond formation. Therefore, mercury does not have a specific crystal structure and is the only metal which is liquid at room temperature with a melting point of -38 degree Celsius.

Distilled water doesn't conduct electricity..

Distilled water does — but very little compared to piped, well or salt water. The reason is that the way a liquid conducts electricity is by the positively or negatively charged ions that are actually moving from one of the electrodes to the other, carrying charge (electricity) with them. Salt water has salt in it, NaCl, which readily ionizes or dissociates to ions of Na+ and Clthat can float through the water carrying charge and thus conduct electricity. Distilled water is water that was boiled to steam and recondensed to water. So distilled water is relatively pure H2O. Water can ionize to H+ and OH- like salt does, but it ionizes to a far lesser degree and is very resistant to conducting electricity.

Orgin of +, - etc symbols...

The earliest print appearance of the modern signs seem to come from a book on Mercantile Arithmetic by Johannes Widmann in 1489, used to indicate surpluses and deficits. The + is a simplification of the Latin “et” (comparable to the ampersand - &). Widmann referred to the symbols - and + as minus and mer. According to the ‘Earliest Uses of Various Mathematical Symbols’ website, a book published by Henricus Grammateus in 1518 used the symbols. Robert Recorde, the designer of the equals sign, introduced plus and minus to the UK in 1557 in The Whetstone of Witte.

Mineral water contain...

Naturally available water, after having come in contact with various salts found in soil stratas and atmosphere, contains a large number of chemicals. Some of them are calcium, magnesium, potassium, sodium, iron, sulphates, nitrates, nitrites, phosphates and oxygen. Small quantities of these substances are responsible for the taste and odour of natural water and are useful for essential functioning of the human body. Very small quantities of copper, chromium, chlorine, fluorine, arsenic, lead, cadmium, mercury and selenium are also found, depending upon the chemistry of the soil.