Answer:
Atomic radius is directly proportional to Metallic reactivity in group 2.
Explanation:
Atomic radius is directly proportional to Metallic reactivity in group 2.
As we move down the group in group 2 which is called as the alkaline earth metals, the atomic number increases due to which the subshell increases. And the outermost shell's electron are less tightly held to the nucleus of the atom. Since the electrons are loosely held that means they can easily participate in reactions and that what makes it reactive down the 2nd group. Therefore alkaline earth metals with higher atomic number are more chemically reactive.
Explanation:
A stable isotope is one that does not emit radiation, or, if it does its half-life is too long to have been measured. It is believed that the stability of the nucleus of an isotope is determined by the ratio of neutrons to protons.
Hope this helps you out : D
Answer:
Valence electrons or outer electrons are most important as they participate in bonding. The octet rule states that atoms gain, lose, or share valence electrons to have filled energy levels.. this gives atoms a stable configuration like that of the nearest noble gas.
Answer:
6s
Explanation:
Barium is in group 2 of the s block and is in period 6.
Answer: (E) 300 bq
Explanation:
Half life is the amount of time taken by a radioactive material to decay to half of its original value.
Radioactive decay process is a type of process in which a less stable nuclei decomposes to a stable nuclei by releasing some radiations or particles like alpha, beta particles or gamma-radiations. The radioactive decay follows first order kinetics.
Half life is represented by 
Half life of Thallium-208 = 3.053 min
Thus after 9 minutes , three half lives will be passed, after ist half life, the activity would be reduced to half of original i.e. 
, after second half life, the activity would be reduced to half of 1200 i.e. 
, and after third half life, the activity would be reduced to half of 600 i.e. 
,
Thus the activity 9 minutes later is 300 bq.
