Question

Question 25
The half-life for a 100-gram sample of radioactive element X is 5 days. How much of element X remains after 10 days have passed?

a
50 g
b
10o g - no change
c
25 g
d
12.5 g
Question 26
What happens to the volume of a gas when the temperature is decreased?

a
The pressure increases.
b
The volume decreases.
c
The volume increases.
d
The mass decreases.

Answer 1

**Question 25:**
The half-life of a radioactive element is the time it takes for half of the substance to decay. Given that the half-life of element X is 5 days, after 10 days (which is 2 half-lives), we can calculate the remaining amount of the sample as follows:

1. After the first half-life (5 days):
\(100 \text{ g} \rightarrow 50 \text{ g}\)

2. After the second half-life (10 days):
\(50 \text{ g} \rightarrow 25 \text{ g}\)

So, the correct answer is **c. 25 g.**

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**Question 26:**
When the temperature of a gas decreases, the volume also typically decreases. This behavior is described by Charles's Law, which states that the volume of a given mass of gas is directly proportional to its temperature (in Kelvin) when the pressure is held constant.

So, the correct answer is **b. The volume decreases.**