Magnesium has atomic no 12
Electronic configuration given by
Or
Answer:- 12 km = 12000 m
Solution:- It's a metric unit conversion where we are asked to convert 12 km to m where km stands for kilometer and m stands for meter.
In metric conversions, kilo means 1000.
So, 1 km = 1000 m
It means, we multiply the given km by 1000 to get the answer in m as:

= 12000 m
Hence, 12 km = 12000 m.
Answer:
particles in 2 moles.
Explanation:
The number of particles that are contained in one mole, the international unit of amount of substance: by definition, exactly 6.022×10²³, and it is dimensionless. It is named after the scientist Amedeo Avogadro.
It is also known as Avogadro's constant.
∴ Number of particles in one mole = 
∴ Number of particles in 2 mole = 2 times Number of particles in one mole
∴ Number of particles in 2 mole=
Hence there are
particles in 2 moles.
0.086mole
Explanation:
The problem is very simple. It involves conversion from mass to number of moles of NaCl
What is mole?
A mole is a unit of measuring chemical substances. It is the amount that contains the avogadro's number of particles.
How is it related and can be converted from mass;
Number of moles of a substance = 
Since we know the mass, we can find the molar mass and put into this equation;
Molar mass of NaCl = 23 + 35.5 = 58.5g/mol
Number of moles of NaCl =
0.086mole
learn more:
Number of moles brainly.com/question/1841136
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The postulate of Dalton's atomic theory which is a result of the law of conservation of mass is: Atoms are indivisible particles, which can neither be created nor destroyed in a chemical reaction.