Answer:
100 g
Explanation:
From the question given above, the following data were obtained:
Original amount (N₀) = 400 g
Time (t) = 4 years
Half-life (t½) = 2 years
Amount remaining (N) =?
Next, we shall determine the number of half-lives that has elapse. This can be obtained as follow:
Time (t) = 4 years
Half-life (t½) = 2 years
Number of half-lives (n) =?
n = t / t½
n = 4 / 2
n = 2
Thus, 2 half-lives has elapsed.
Finally, we shall determine the amount remaining of the radioactive isotope. This can be obtained as follow:
Original amount (N₀) = 400 g
Number of half-lives (n) = 2
Amount remaining (N) =?
N = 1/2ⁿ × N₀
N = 1/2² × 400
N = 1/4 × 400
N = 0.25 × 400
N = 100 g
Thus, the amount of the radioactive isotope remaing is the 100 g.
Cutting of Nails is a Physical Change since no new substance is formed.
Don't confuse it with Reversible and Irreversible Changes
First, we determine the moles of Mg(NO₃)₂ present:
moles = mass / Mr
= 46.5 / (24 + 2 x (14 + 16 x 3))
= 0.4 mole
Each mole of Mg(NO₃)₂ contains 2 moles of Nitrogen atoms.
Moles Nitrogen = 0.4 x 2
= 0.8 mole
Answer:
The core turns its hydrogen to helium and stops nuclear fusion which causes the outer shells of hydrogen to collapse.
Explanation:
This results in higher temperature and pressure which in turn causes the outer shells to expand and cool as a red giant.
