20 because
mass no=electrons+neutrons
so to find neutrons
mass no-electrons=neutron

Density is defined as Mass per unit volume of an object ~
And hence, the correct choice is ~ 1


Answer:Magnesium (Mg) is a - reactant
Hydrogen (H2) is a - product
magnesium chloride (MgCI2) is a - product
hydrochloric acid (HCI) is a - reactant
Explanation: It’s in my notes