Which of the following statements regarding radiation are false?

a. all elements heavier than bismuth are radioactive.
b. the time for half of the original sample to spontaneously decay is called the half-life (t1/2).
c. all radioactive elements are spontaneously decaying towards formation of a stable element.
d. radioactivity is a natural part of our environment. all of the above are true.

All of the given statements are true.

Explanation:

All the elements are heavier than Bismuth (Bi) are radioactive.

The time for half of the original sample to spontaneous decay is called half life ()

All radioactive elements are spontaneously decaying towards formation of a stable element.

Radioactive elements undergo decay in order to attain stability.

Radioactivity is a natural part of our environment. The earth also contains several primordial long-lived radioisotopes that have survived to the present in significant amounts.

Hence, all the given statements are true.

there is none because earth is stationary and flat.