4) The charred bones of a sloth in a cave in Chile represent the earliest evidence of human presence in the
southern tip of South America. A sample of the bone has a C-14 activity of 5.22 disintegrations per minute
per gram of carbon. If the C-14 activity in living organisms has an activity of 15.3 disintegrations per minute
per gram of carbon, how old are the bones? (the half-life of C-14 is 5730 years).

Explanation:

Half-life is the number of years it takes for a quantity of a substance to decompose in half.

You may measure the amount of the substance in mass, concentration, or activity, among others.

Thus, if you start with an amount A₀ of a substance that decays with a contstan half-life, the amount, A, remaining after passing n half-lives will be:

Then, if you know the initial amount,A₀, and the current amount remaining, A, of a substance, you can calculate the number of half-lives elapsed.

In this case:

Thus:

Hence, about 1.55 half-lives have elapsed since the organism died.

Since the half-life of C-14 is 5,730 years, the bones are 1.55 × 5,730 = 8,881.5 ≈ 8,880 years old ← answer.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.