IUPAC (International Union for Pure and Applied Chemistry) has rules for writing chemical symbols and formulas. They are valid in all languages.
For compounds search in a library Nomenclature of inorganic compounds and Nomenclature of organic compounds, with the text adapted to your language, if necessary.
See the links below.
The correct way to write the symbol for magnesium is Mg (uppercase M, lowercase g).
The correct way to write it is ' 120 '.The correct way to say it is "One hundred twenty".
Chemicals symbols of elements are writed after the rules of IUPAC; see a list at the link below.
The correct way to write fireplace is as one word - "fireplace."
Feet use the symbol ' Inches use the symbol " 28' is correct
the correct way is to simply write 3 and a colon following it then write down 2 zeroes followed by hrs
The correct way to write 95 in standard form is 9.5 × 101
1012 is the correct way to write it but if you mean in words the 1 thousand and twelfth
In English, either way of saying this phrase is correct.
In AP style, temperatures should be written with numerals and the degree symbol, such as 32F for Fahrenheit or 0C for Celsius.
Correct writing: 23994Pu (but is recommended to use an equation editor).
The correct way is to write New Year's Eve.