Which of the following is the correct order of decreasing reactivity? A. Iron, potassium, magnesium, gold, copper
B. Magnesium, copper, iron, gold, potassium
C. Gold, potassium, iron, copper, magnesium
D. Potassium, magnesium, iron, copper, gold

The decreasing order of chemical reactivity is given below.

(most active) Na > Ca > Mg > Zn > Fe > Cu (least active)

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.