B) energy is absorbed by the reaction
is right answer.
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.
I believe the answer is a because 2 times 12 is 24. Hope this helped
Answer: Boron is the element which has properties of both metals and nonmetals.
Explanation:
Metals are defined as the elements which loose electrons to attain stable electronic configuration. They attain positive charge and form cation. Example: Zinc (Zn), Aluminium (Al) , copper (Cu)
Non-metals are defined as the elements which gain electrons to attain stable electronic configuration. They attain negative charge and form anion. Example: Chlorine (Cl) , Sulphur (S)
Metalloids are defined as the elements which show properties of both metals and non-metals. There are 7 metalloids in the periodic table. They are Boron (B) , Silicon (Si) , Germanium (Ge) , Arsenic (As) , Antimony (Sb), Tellurium (Te) and Polonium (Po).
Thus boron is the element which has properties of both metals and nonmetals.
