The correct answer is option B. Where are the regions of electron density?
In the quantum mechanical model of the atom the exact location of an electron is unknown. But there is a probability of finding an electron in a given space. So in quantum mechanics instead of an electron we always refer to electron density, which is simply the probability of finding an electron in space.
Answer: a. solution
Explanation:
A solution is a mixture which contains two or more than two types of components and they can be separated by physical means as well.Example: salt water
Molecule of an element is defined as the aggregate of atoms of similar elements. Example:
. Molecule of a compound is the aggregate of atoms of different elements in a fixed ratio by mass. Example: 
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: 
A pure substance is a substance which contains definite composition of only one type of component. Hence, it cannot be separated by physical means. Example: Helium, water
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Question: Which of the following is most likely an indication of a chemical change?
Answer Choices:
A. A loud sound when an MP3 player is turned on.
B. A loud sound when someone claps their hands.
C. A loud sound when a starter's pistol is fired at a race.
D. A loud sound when a large object falls to the ground.
Correct Answer:
C. A loud sound when a starter's pistol is fired at a race.
Reasons:
A would not be correct since an MP3 player is a mechanical object and does not mix any substances that create a reaction.
B would not be correct since clapping hands causes a loud sound due to two forces slamming together and causes a disturbance in the air.
D would not be correct since a large object falling to the ground does not indicate any chemical reactions or changes since its merely the result of a mass hitting another mass.
C would be correct since the gunpowder mixes with other substances inside the pistol's chamber and causes and explosion, and explosions are part of a chemical reaction indicators.
Answer:
0.020 mol
Explanation:
Let's consider the following relations:
- 20 drops of a liquid have a volume of 1 mL.
- The density of the solution is 1.685 g/mL, that is, each milliliter of solution has a mass of 1.685 g of solution.
- There are 85 g of phosphoric acid per 100 grams of solution (85 % by weight).
- The molar mass of phosphoric acid is 97.99 g/mol
With these relations, we can calculate the moles of phosphoric acid in 27 drops of solution.

Answer:
ACE
Explanation:
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