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.
7. Atomic mass
8. Atomic number
9. Chemical symbol
10. Right
To completely convert 9. 0 moles of hydrogen gas (h2) to ammonia gas, 3.0 moles of nitrogen gas (n2) are required.
<h3>What are moles?</h3>
The mole is a SI unit of measurement that is used to calculate the quantity of any substance.
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The given reaction is 
By the stoichiometry rule of ratio hydrogen: nitrogen
3 : 1
The reacted moles of nitrogen is equals to H/3 moles of reacted hydrogen
So, moles of nitrogen

Thus, 3.0 moles of nitrogen gas (n2) are required.
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