Question

why magnesium ribbon start floating in water​

Answer 1

Answer:

because it has an oxide layer on it

Answer 2

Answer:Magnesium hydroxide being insoluble in water deposits on the surface of the magnesium ribbon and cuts off the contact of magnesium with water and the reaction stops. Hydrogen gas bubbles formed on the surface of the magnesium ribbon makes it lighter than water. Hence magnesium ribbon floats on water.