Number of atoms : 1.26 x 10²³
<h3>Further explanation </h3>
The mole is the number of particles(molecules, atoms, ions) contained in a substance
1 mol = 6.02.10²³ particles
Can be formulated
N=n x No
N = number of particles
n = mol
No = Avogadro's = 6.02.10²³
0.21 moles of Al, so n = 0.21
Number of atoms :

By looking at it and if it is making a single movement it is moving.
NH3 = water (it is actually a water soluble gas)
C6H14 = CCl4 (C6H14 won't mix with water at all)
Na2S = water (Na2S is a salt. Salts dissolve best in water)
Br2 = CCl4, but it will also dissolve in water.
I think it would be taxonomy which is the the classification of something. Mostly organisms.
Answer:
How much energy would be produced from the reaction of 2.40 moles hydrogen with 3.95 moles chlorine?

Explanation:
Given,
2.40 moles hydrogen reacts with 3.95 moles chlorine.
From the balanced chemical equation,
1mol. of H2 reacts with 1mol. of Cl2
then,
2.40mol. of H2 reacts with ----?mol of Cl2

So, the remaining moles of Cl2 is in excess.
The limiting reagent is--- H2.
1mol. of H2 releases --- 554kJ of energy
then,
2.40mol of H2 releases ---- ?

Answer is: deltaH =-1329.6kJ