Half-life of a radioactive substance is the time required to reduce the amount of substance to half of its initial amount.
In present case, half-life is material is given as 1000 years and initial amount of material is given as 400 kg
Answer 1) Since, half-life of radio-active substance is 1000 years, therefore after 1st half life, amount of the material will be left to half the initial amount. Hence, amount of substance left after 1000 years = 400/2 = 200 kg.
Answer 2) For 2000 years, radioactive material has crossed 2 times the half life. Therefore , amount of the material will be left to 1/4 the initial amount. Hence, amount of substance left after 2000 years = 400/4 = 100 kg.
Answer 3) For 4000 years, radioactive material has crossed 4 times the half life. Therefore , amount of the material will be left to 1/16 the initial amount. Hence, amount of substance left after 4000 years = 400/16 = 25 kg.
Chemists, biologist, pharmacist, medical researcher ect…
Answer:One mole of HBr has 6.02 x 1
0
23
molecules of HBr.
1 mole of HBr = 6.02 x 1
0
23
molecules of HBr.-----(a)
X mole of HBr has 1.21 x
10
24
molecules of HBr.
X mole of HBr = 1.21 x
10
24
molecules of HBr------(b)
Taking ratio of (a) and (b)
X / 1 = 1.21 x
10
24
/ 6.02 x 1
0
23
X= 2.009 moles.
Explanation:
