Question

90% of the active nuclei present in a radioactive sample are found to remain undecayed after 1 day. The percentage of undecayed nuclei left after two days will be

• A. 85 %
• B. 81 %
• C. 80 %
• D. 79 %

Answer 1

The correct option is B 81 %

It can be clearly said that the nuclei got decayed by 10% per day , which implies that,

$100\underset{10\%}{\overset{1day}{\to }}90\underset{10\%}{\overset{1day}{\to }}81$