Answer:
I think option (d) is right answer
Answer:

Explanation:
The question will be easier to solve if we interpret it as, " How long will it take until one-fourth of a sample of the element remains,?"
The half-life of the element is the time it takes for half of it to decay.
After one half-life, half (50 %) of the original amount will remain.
After a second half-life, half of that amount (25 %) will remain, and so on.
We can construct a table as follows:


Answer:
0.84 mol
Explanation:
Given data:
Moles of ZnCl₂ produced = ?
Mass of Zn = 55.0 g
Solution:
Chemical equation:
2HCl + Zn → ZnCl₂ + H₂
Number of moles of Zn:
Number of moles = mass / molar mass
Number of moles = 55.0 g/ 65.38 g/mol
Number of moles = 0.84 mol
Now we will compare the moles of Zn with ZnCl₂ from balance chemical equation.
Zn : ZnCl₂
1 : 1
0.84 : 0.84
So from 55 g of Zn 0.84 moles of zinc chloride will be produced.