Answer:- 448 mL of hydrogen gas are formed.
Solution:- It asks to calculate the volume of hydrogen gas formed in milliliters at STP when 0.020 moles of magnesium reacts with excess HCl acid. The balanced equation is:

There is 1:1 mol ratio between Mg and hydrogen gas. So, the moles of hydrogen gas is also equals to the moles of Mg reacted.
moles of Hydrogen gas formed = 0.020 mol
At STP, volume of 1 mol of the gas is 22.4 L. We need to calculate the volume of 0.02 moles of hydrogen gas.

= 0.448 L
They want answer in mL. So, let's convert L to mL using the conversion formula, 1L = 1000mL

= 448 mL
So, 0.020 moles of magnesium would produce 448 mL of hydrogen gas at STP on reacting with excess of HCl acid.
The element is Sodium with an atomic number of 11 and electrovalent bonding takes place when it comes near an atom having seven valence electrons.
<h3>What is Electrovalent bonding?</h3>
This is also referred to as ionic bonding and involves the transfer of atoms of an element to another.
In order for both of them to achieve a stable octet configuration, sodium donates one atom to the element seven valence electrons.
Read more about Electrovalent bonding here brainly.com/question/1979431
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During the chemical reaction, the solid substance that is insoluble formed during the combination of two aqueous solutions is called a precipitate. The answer is letter C. The precipitation reaction occurs when a salt is formed in the reaction of solutions with salts.
According to the law of conservation of mass, the quantity of the elements, involved in chemical reactions does not change. For example,
H2O2 - > H2O + O2
is wrong, because there are two O atoms on the first side of the equation, and three on the other. To correct it, coefficients must be added, until the amount of both H and O atoms is equal on both sides.
2H2O2 - > 2H2O + O2
In order for a solute to dissolve in a solvent,
the attractive forces between solute particles and the solvent particles must
be stronger than the attractive forces between solute-solute and
solvent-solvent particles. This is important so that the solute will remain in
solution.