Answer: The answer for this is Compound.
Explanation: A matter is something which occupies space and has some mass.
Elements are defined as the smallest substances which cannot be broken down into another substance by any chemical means.
A compound is a defined as a substance composed of two or more different elements when they combine chemically in definite proportion. For example: 
is named as carbon dioxide and is a compound made by combining carbon and oxygen in a fixed ratio of 1 : 2
So, the answer to the given question is compound.
Given by the name of these compounds, they are formed if one or more hydrogen atoms are substituted for halogens
X = Cl, Br, I, F
Dmitri Mendeleev invented the periodic table.
If I study, I will pass the exams.
The volume (in liters) of CO₂ that can be consumed at STP by 435 g Na₂O₂ is 125 L of Co₂
<u><em>calculation</em></u>
2Na₂O₂(s) +2 CO₂ (g)→ 2 Na₂CO₃(s) + O₂(g)
Step 1 : find the moles of Na₂O₂
moles = mass÷ molar mass
from periodic table the molar mass of Na₂O₂ = (23 x2) +( 16 x2) = 78 g/mol
moles= 435 g÷ 78 g/mol = 5.58 moles
Step 2: use the mole ratio to determine the moles of CO₂
from given equation Na₂O₂ : CO₂ =2 :2 =1:1
Therefore the moles of CO₂ is also = 5.58 moles
Step 3: find the volume of CO₂ at STP
that is at STP 1 mole of a gas = 22.4 L
5.58 moles = ? l
<em>by cross multiplication</em>
= (5.58 moles x 22.4 L) / 1 mole = 125 L
