Question

how many neutrons are in the most common isotope of chlorine: chlorine-35
17 neutrons
18 neutrons
35 neutrons
there is not enough information to solve this.
true or false: there is only one mass number for each element. *
true
false
a college student drinks caffeine (half - life is 6 hours). how long will it take for there to be 25% of it left in their body?
immediately
3 hours
6 hours
9 hours
12 hours

Explanation:

First Question

Step1: Recall atomic number of Chlorine

The atomic number of Chlorine (\(Cl\)) is \(17\).

Step2: Use formula for number of neutrons

Number of neutrons \(N=\text{Mass number}-\text{Atomic number}\). For Chlorine - 35, mass number \(A = 35\), atomic number \(Z=17\). So \(N=35 - 17\).

Step3: Calculate the value

\(N=18\)

Isotopes of an element have different mass numbers. For example, Chlorine has \(Cl - 35\) and \(Cl - 37\). So, there is not only one mass number for each element.

Step1: Use half - life formula

The formula for the amount of a substance remaining after \(n\) half - lives is \(N = N_0\times(\frac{1}{2})^n\), where \(N\) is the final amount, \(N_0\) is the initial amount. We want \(N = 0.25N_0\). So, \(0.25N_0=N_0\times(\frac{1}{2})^n\).

Step2: Solve for \(n\)

Dividing both sides by \(N_0\) (since \(N_0
eq0\)), we get \(0.25 = (\frac{1}{2})^n\). We know that \((\frac{1}{2})^2=\frac{1}{4}=0.25\), so \(n = 2\).

Step3: Calculate time

Since the half - life \(t_{1/2}=6\) hours and \(t=n\times t_{1/2}\), then \(t = 2\times6\) hours.

Answer:

18 neutrons

Second Question