Question

The half life period of a radioactive substance is 140 days. After how much time, 15 gm will decay from a 16 gm sample of the substance?–

• A. 140 days
• B. 560 days
• C. 420 days
• D. 280 days

Answer 1

Answer: (B)

560 days

Answer 2

= $\frac { 1 \mathrm { gm } } { 16 \mathrm { gm } }$ = $\left( \frac { 1 } { 2 } \right) ^ { 4 }$ = $\left( \frac { 1 } { 2 } \right) ^ { \frac { \mathrm { t } } { \mathrm { T } } }$ Ž t = 4T = 4×140 days

= 560 days