Answer:
Explanation:
The half life of a radioactive atom is the time taken for half of the radioactive nuclei to disintegrate. The shorter the half life, the faster a radioactive nuclei decays.
Half life is often expressed as:
Half life = 
Where λ is the decay constant.
Watershed
A watershed is an entire river system of an area drained by a river and its tributaries
Answer:
B)
Explanation:
Electronic shell 2s2 2p6
Maximum level of electronic shell represents in which period is located that element