Among alkali metals, radioactive element is ---- and half-life period of its longest lived isotope is (A) Francium and 21 years (B) Radium and 21 minutes (C) Francium and 21 minutes (D) Radium and 21 days

1.0 g of a radioactive isotope left 125 mg after 24 hr. The half-life period of the isotope is a. 8 hr b. 24 hr c. 6 hr d. 4 hr

Calculate the half-life period of a radioactive element which remains only 1/16 of it's original amount in 4740 years. ( A) 1185 years ( B) 2370 years (C) 52.5 years (D) none of these

Calculate the half-life period of a radioactive element which remains only 1/16 of it's original amount in 4740 years. ( A) 1185 years ( B) 2370 years (C) 52.5 years (D) none of these

Radium has a half life 1600 years and its daughter elements radon has a half life 3.82 days. In an enclosure, the volume of radon was found constant for a week. Explain and calculate the ratio of the number of radium and radon nuclei. Will the ratio be constant after 400 years?

Radioactive elements decays at such a rate that after 68 minutes only one-fourth of its original amount remains. Calculate its decay constant and half life period.

Read the following : (i) The half-life period of a radioactive element X is same as the mean-life time of another radioactive element Y. Initially both of them have the same number of atoms. Then Y will decay at a faster rate the X. (ii) The electron emitted in beta radiation originates from decays of a neutron in a nucleus (iii) The half-life "of"^( 215) At is 100 ms. The time taken for the radioactivity of a sample "of"^( 215) At to decay to 1//16^(th) of its initial value is 400 ms. (iv) The volume (V) and mass (m) of a nucleus are related a V prop m. (v) Given a sample of Radium - 226 having halflife of 4 days. Find the probability, a nucleus disintegrates within 2 half lives is 3/4. Select the correct code for above.

(a) A radioactive sample has 6.0 xx 10^(18) active nuclei at a certain instant. How many of these nuclei will still be the same active state after two half-lives? (b) Radioactive phosphours -32 has a half-life of 14 days. A source containing this isotope has an initial activity of 10muCi . (i) What is the activity of the source after 42 days? (ii) What time elapse before the activity of the source falls at 2.5muCi ? (c) 1g of a radioactive substance disintergrates at the rate of 3.7 xx 10^(10) dps . The atomis mass of the substance is 226 . Calculate its mean life.

The half life period of a radioactive element is 10 days. Then how long does it take for 90% of a given mass of this elements to disintegrate -A) 19 days B) 27 days C) 33 days -D) 47 days