Answer:- 
molecules.
Solution:- The grams of tetrabromomethane are given and it asks to calculate the number of molecules.
It is a two step unit conversion problem. In the first step, grams are converted to moles on dividing the grams by molar mass.
In second step, the moles are converted to molecules on multiplying by Avogadro number.
Molar mass of 
= 12+4(79.9) = 331.6 g per mol
let's make the set up using dimensional analysis:
= molecules
So, there will be molecules in 250 grams of .
Chemists use balanced chemical equations as a basis to calculate how much reactant is needed or how much product will be formed in a reaction.
<u>We are given:</u>
Mass of NaCl in the given solution = 22.3 grams
Volume of the given solution = 2 L
<u></u>
<u>Number of Moles of NaCl:</u>
We know that the number of moles = Given mass / Molar mass
Number of moles = 22.3 / 58.44 = 0.382 moles
<u></u>
<u>Molarity of NaCl in the Given solution:</u>
We know that Molarity of a solution = Moles of Solute / Volume of Solution(in L)
Molarity = 0.382 / 2
Molarity = 0.191 M
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1.it is readily available since hydrogen is a basic earth element and it's very abundant.
2. It doesn't produce harmful emissions.
Disadvantages
1.it is expensive. It is expensive because it takes a lot of time to separate the element from others.
2.it is difficult to store. Even moving a tiny bit of hydrogen would be very expensive.
3. It is highly flammable. Since it is a very powerful source of fuel, hydrogen can be very flammable.
