Answer:
The true statement is:
They are formed when atoms of different elements combine.
Explanation:
Compounds are formed when atoms of different elements combine.
Atoms of different elements combine with each other to attain stable electronic configuration.
The atoms can combine with each other in two different ways:
1) By sharing the electrons
2) By exchanging electrons
When they share electrons with each other, they form a covalent bond.
When they exchange electrons, they form an ionic bond.
Answer:
8 moles
Explanation:
When we are asked to convert from grams of a substance into moles, we have to use the substance's molar mass.
Meaning that for this problem, we'll <em>use the molar mass of hydrogen peroxide</em> (H₂O₂), as follows:
There are 8 moles in 272 grams of hydrogen peroxide.
ANSWER:
4 a) Specific elements have more than one oxidation state, demonstrating variable valency.
For example, the following transition metals demonstrate varied valence states:
,
,
, etc.
Normal metals such as
also show variable valencies. Certain non-metals are also found to show more than one valence state 
4 b) Isotopes are members of a family of an element that all have the same number of protons but different numbers of neutrons.
For example, Carbon-14 is a naturally occurring radioactive isotope of carbon, having six protons and eight neutrons in the nucleus. However, C-14 does not last forever and there will come a time when it loses its extra neutrons and becomes Carbon-12.
5 a)
→
5 b)
→ 
5 c)
→
(already balanced so don't need to change)
5 d)
→
5 e)
→ 
EXPLANATION (IF NEEDED):
1. Write out how many atoms of each element is on the left (reactant side) and right (product side) of the arrow.
2. Start multiplying each side accordingly to try to get atoms of the elements on both sides equal.
EXAMPLE OF BALANCING:
The volume of N₂ at STP=56 L
<h3>Further explanation</h3>
Given
2.5 moles of N₂
Required
The volume of the gas
Solution
Conditions at T 0 ° C and P 1 atm are stated by STP (Standard Temperature and Pressure). At STP, the volume per mole of gas or the molar volume-Vm is 22.4 liters/mol.
So for 2.5 moles gas :

Answer:
I don't understand what you are asking