The sum of the number m and 7.1
(write it in a algebra expression? )

In mathematics when we use the numbers and letters to show the relationship between two quantities, the expression is called algebraic expression.

The sum of the M and 7.1 is M+7.1

We don’t know the value of M so we don’t know the exact value for sum of M and 7.1

When we writ this in algebraic expression,

 let S is the sum of M and 7.1

then the equation will be:

M  + 7.1 = N

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.