The new substance form in a chemical reaction:

The correct option is B

Product

The explanation for the correct option:

Chemical reactions: A chemical reaction is in which the bonds are broken within reactant molecules, and new bonds are formed within product molecules in order to form a new substance.

• An example of a chemical reaction is the reaction of Magnesium($\mathrm{Mg}$) with Oxygen(${\mathrm{O}}_2$) results in the formation of Magnesium oxide($\mathrm{MgO}$)
• $\underset{\mathrm{Magnesium}}{2\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Magnesium}\mathrm{oxide}}{2\mathrm{MgO}\left(\mathrm{s}\right)}$

(B) Product: The substance which is formed in a chemical reaction is called the product.

• In the above reaction, Magnesium oxide($\mathrm{MgO}$) is the product.

The explanation for the incorrect option:

(A) Reactant: The substance which takes part in a chemical reaction is called a reactant.

• In above reaction, Magnesium($\mathrm{Mg}$) with Oxygen(${\mathrm{O}}_2$) are reactant.

(C)Equation: Chemical equations are symbolic representations of chemical reactions in which the reactants and the products are expressed in terms of their respective chemical formulae.

• Example, $\underset{\mathrm{Magnesium}}{2\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Magnesium}\mathrm{oxide}}{2\mathrm{MgO}\left(\mathrm{s}\right)}$

Therefore, option(B) is correct option.