A. The atmosphere
All the other examples are either elements or compounds, not mixtures. A mixture is a combination of elements that are not chemically or irreversibly conjoined so the atmosphere, made up of a variety of gases, would be a mixture.
The atoms of different chemical elements can be differentiated based on the number of protons.
Each chemical element is differentiated by his number of protons. This number of protons is also knowing as atomic number and it is represented by the letter (Z).
The atomic number represented the number of protons in the nucleus of an element. For example:
- The element that has only 1 proton in his nucleus is Hydrogen atom.
- The element that has 2 protons in his nucleus is Helium atom.
<h3>What is an atom?</h3>
The atom is the smallest part of the composition of matter, it is indivisible and is composed of a nucleus that has protons and neutrons, and around the nucleus there are the electrons.
Learn more about the atom at: brainly.com/question/17545314
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The electron dot diagram tells
us about how many electrons are being shared between atoms. Also, the number of
valence electron to be shared corresponds to the group number the element
belongs. Say for example H2O, hydrogen has one valence electron and oxygen has
two valence electrons.
Answer:- 0.134 seconds
Solution:- The speed is given as 
and the circumference is 24900 miles which is same as the distance light have to covered. It asks to calculate the time required to cover this distance by the light.
We need to do unit conversion from miles to meter as the speed is given in meter per second.
1 mile = 1609.34 meter
So, 
= 40072566 meters
Know that, 
It's rearranged to time as, 
Let's plug in the values in it:
= 0.134 seconds
So, the light would take 0.134 seconds to travel the mentioned speed. The answer without the unit is 0.134.
<h3>
Answer:</h3>
0.643 moles
<h3>
Explanation:</h3>
We are given;
Density of nitrogen gas as 1.20 g/L
Volume nitrogen as 15.0 L
We are required to calculate the number moles of nitrogen gas;
<h3>Step 1: Determine the mass of nitrogen gas</h3>
We know the density is given by dividing mass by volume.
Therefore, to get the mass;
- Mass = Density × volume
- Mass = 1.20 g/L × 15.0 L
= 18 g
<h3>Step 2: Determine the mass of nitrogen gas </h3>
We know that to get the number of moles, we divide mass by molar mass;
That is, moles = Mass ÷ Molar mass
But, molar mass of nitrogen gas is 28 g/mol
Therefore;
Moles of nitrogen gas = 18 g ÷ 28 g/mol
= 0.643 moles
Therefore, the number of moles of nitrogen gas 0.643 moles
