Molarity's formula is known as: Molarity(M)=moles of solute/liters solution.
In this case we are already given moles and liters so you just have to plug the numbers into the equation.
0.400 mol HCL/9.79L solution=0.040858M
If you were to use scientific notation, the answer will be: 4.1*10^-2, but otherwise, you can just use the decimals above and round appropriately as you see fit.
Answer: The new concentration of a solution of
is 0.2 M 10.0 mL of a 2.0 M
solution is diluted to 100 mL.
Explanation:
Given:
= 10.0 mL,
= 2.0 M
= 100 mL,
= ?
Formula used to calculate the new concentration is as follows.

Substitute the values into above formula as follows.

Thus, we can conclude that the new concentration of a solution of
is 0.2 M 10.0 mL of a 2.0 M
solution is diluted to 100 mL.
Answer: The correct answer is option B i.e., 2.78 mol
Explanation:
Aluminium reacts with iodine to form Aluminium iodide

From the equation, it is clear that 3 moles of iodine reacts with 2 moles of Aluminium to form Aluminium iodide
We know
For 2 moles of Aluminium, 
3 moles of Iodine reacts with 54 g of Aluminium
? moles of iodine react with 50 g of Aluminium
Solid should be the anwser