Question

When chemists write out reactions, they often place numbers to the left of a chemical formula.

Answer 1

 The  number  to the   left   of  a chemical  formula is  called   coefficients

 Explanation

Coefficient  is  the  number in  front  of a chemical  formula.

It tell  how many  molecules  of a given formula that are  involved  in a chemical  reaction.

in   2H+O→  H2O  the coefficient  are  2,1,1

that is, 2  in front  of H2

            1 in front of O

               1 in  front of H2O

Answer 2

Answer: The correct answer is coefficients.

Explanation:

Coefficients are defined as the numbers which are written in front of the atoms or molecules in a chemical reaction. They represent the number of moles of substance in a chemical reaction.

Subscript numbers are defined as the number of atoms of each element present in a compound.

Superscript numbers are defined as the charges of ions reacting in a chemical reaction.

For Example: Dissociation of sodium carbonate into its ions, the equation follows:

$Na_2CO_3\rightarrow 2Na^++CO_3^{2-}$

The number '2' on the left side written in the subscript of sodium ion represents the number of sodium atoms.

The number '2' on right side written in front of sodium ion represents the number of moles of sodium ions.

The number '(2-)' on right side written in the superscript of carbonate ion represents the charge on carbonate ion.

Hence, the correct answer is coefficients.