Which statement about the half-life of a radioactive sample is true?
O It is an exact measure of the decay of an individual atom.
O It measures the tendency of a radioisotope to decay radioactively
O It is affected by the concentration of the radioactive substance that is present
It can be calculated based on neutron number

Explanation:

The half life period of any radio active substance is the time required to decay half of its total quantity . Thus it measures the tendency of a radioactive substance to decay .

It is independent of the original quantity of matter present .

B

Explanation:

edg

d₁ = displacement of tern from arctic to antarctic = 11000 miles

d₂ = displacement of tern from antarctic to arctic =   - 11000 miles

d = total displacement for the journey

total displacement for the journey is given as

d = d₁ + d₂

d = 11000 + (-11000)

d = 0 miles

t₁ = time of travel from arctic to antarctic = 3 months = 3 x 30 days = 90 days

t₂ = time of travel from antarctic to arctic = 3 months = 3 x 30 days = 90 days

t = total time of travel

total time of travel is given as

t = t₁ + t₂

t = 90 + 90

t = 180 days

average velocity is given as

average velocity = total displacement/ total time

v = d/t

v = 0/180

v = 0 miles/day

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.