After 3 half-lives, 125 grams of the parent isotope will remain.
The correct answer is B. The nitrogen in the nitrogen cycle originate from the atmosphere. It forms approximately 78% of the Earth's atmosphere. However, this form is not usable because it is in its most stable form therefore unreactive. This nitrogen gas needs to be converted into nitrate compound for it to be usable. Then, the nitrogen cycle starts.<span />
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The initial temperature of the water that resulted in the final temperature of the water-metal mixture is 20.7 ⁰C.
<em>"Your question is not complete, it seems to be missing the following information;"</em>
the specific heat capacity of the metal is 0.45 J/g⁰C.
The given parameters;
- <em>mass of water, </em>
<em> = 45 g</em> - <em>final temperature of the water, </em>
<em> = 22 ⁰C</em> - <em>mass of the metal, m = 8.5 g</em>
- <em>initial temperature of the metal, t = 82 ⁰C.</em>
- <em>specific heat capacity of the metal, c = 0.45 J/g⁰C.</em>
The initial temperature of the water will be calculated by applying the principle of conservation of energy;
<em>heat gained by water = heat lost by metal</em>


where;
<em>is the specific heat capacity of the water = 4.184 J/g⁰C.</em>
<em />
<em>Substitute the given values;</em>
45 x 4.184 x (22 - t) = 8.5 x 0.45 x (85 - 22)
4142.16 - 188.28t = 240.98
188.28t = 4142.16 - 240.98
188.28t = 3901.18

Thus, the initial temperature of the water that resulted in the final temperature of the water-metal mixture is 20.7 ⁰C.
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