Pure substances that cannot be broken down into other substances by any chemical or physical means are known as element.
Pure substances that can be broken down into elements by any chemical or physical means are known as compounds.
Combination of pure substances in which they retain their properties is known as mixture.
Mixtures in which the components of mixture are uniformly distributed are known as homogeneous mixture whereas mixtures in which its components are can be easily seen are known as heterogeneous mixture.
Since propane, 
is made up of two different elements that is carbon, 
and hydrogen, 
. There are 3 carbon and 8 hydrogen atoms present in the propane molecule.
So, it is a compound.
phosphorus in water is rapid combustion.
Answer:
3.612 × 10^24 molecules
Explanation:
The balanced chemical equation in this question is given as;
2Al + 6HCl → 2AlCl3 + 3H2
Based on the equation, 2 moles of Aluminum (Al) is needed to react with 6 moles of HCl
Since 1 mole of a substance is equal to 6.02 × 10^23 molecules;
This means that, according to the question, 6 moles of HCl needed to react with 2 moles of Al will contain;
6 × 6.02 × 10^23 molecules
= 36.12 × 10^23
= 3.612 × 10^24 molecules
In a nutshell, 3.612 × 10^24 molecules of HCl would react with 2 moles of Al.
