The half-life of a radioactive element is the amount of time it ...

[notis]

The half-life of a radioactive element is the amount of time it takes for ___________________ _ of the
  atoms of the unstable ___________________ _ element to decay to atoms of a new, more stable
  ___________________ _ element. Fill in the blank(s) with the appropriate word(s).

Question 2

Different varieties of an atom that have a different number of neutrons in their nuclei are
  ___________________ _.c Fill in the blank(s) with the appropriate word(s).

[xMRAZ]

Answer to Question 1

half, parent, daughter

Answer to Question 2

isotopes

[notis]

Excellent

[momolu]

Gracias!