Answer:

Explanation:
The expression can be solved mathematically as follows:
1)
Given
2)
Definition of sum
3)
/Associative property
4)
Distributive property
5)
Multiplication
6)
Subtraction.
7)
Multiplication/Associative property
8)
Associative property
9)
/Result
Answer:
Explanation:B ice melting is a phiyscal change and the mass of the substance remains the same
Answer:
Explanation:
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope is ²³Na. The free metal does not occur in nature, and must be prepared from compounds.
Answer: 72 grams of
are needed to completely burn 19.7 g 
Explanation:
According to avogadro's law, 1 mole of every substance weighs equal to molecular mass and contains avogadro's number
of particles.
To calculate the number of moles, we use the equation:

Putting in the values we get:


According to stoichiometry:
1 mole of
requires 5 moles of oxygen
0.45 moles of
require=
moles of oxygen
Mass of 
72 grams of
are needed to completely burn 19.7 g 