Lead fluoride hope this helps
Mass of this substance = 9.928 g
<h3>Further explanation</h3>
Molarity is a way to express the concentration of the solution
Molarity shows the number of moles of solute in every 1 liter of solute or mmol in each ml of solution

Where
M = Molarity
n = Number of moles of solute
V = Volume of solution
So to find the number of moles can be expressed as

mol of substance -Lithium nitrite - LiNO₂ :
V = 250 ml = 0.25 L
M = 0.75 M

So mass of this substance - LiNO₂ (MW=52,947 g/mol) :

Answer : The concentration of A after 80 min is, 0.100 M
Explanation :
Half-life = 20 min
First we have to calculate the rate constant, we use the formula :



Expression for rate law for first order kinetics is given by:

where,
k = rate constant = 
t = time passed by the sample = 80 min
a = initial amount of the reactant = 1.6 M
a - x = amount left after decay process = ?
Now put all the given values in above equation, we get


Therefore, the concentration of A after 80 min is, 0.100 M
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