They use fans and air conditioning in the summer because its hot, which means they use energy and in the winter, there is no need because its cold so less energy.
Answer:
the abbreviation form of full name is called symbol.
the smallest unit of cimpound is called molecule.
For which of the following activities might you want to hire a chemist?
Answer: D. testing a rock sample for gold content
Which of the following procedures involves a physical change in one of the substances?
Answer: C. separating a salt solution by evaporating the water
Answer:
It is an amorphous solid and hence also called pseudo solid. So it flows very slowly over thousands of years. It is not visible to the n*ked eye.
1.51 x 10²⁵atoms
Explanation:
Given parameters:
Mass of Na = 578g
Unknown:
Number of atoms = ?
Solution:
To find the number of atoms, we must first find the number of moles the given mass contains.
Number of moles = 
molar mass of Na = 23g
Number of moles =
= 25.13moles
1 mole of a substance = 6.02 x 10²³atoms
25.13 mole of Na = 25.13 x 6.02 x 10²³atoms
This gives 1.51 x 10²⁵atoms of Na
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Avogadro's constant brainly.com/question/2746374
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