78 grams of a radioactive nuclei x undergoes radioactive decay. the half-life of x is 4.7 minutes. after 16.5 minutes, the remaining sample of x is approximately: 12.8g ; 8.4g ; 6.9g ; 5.5g ;

The remaining sample of X is 6.9 grams.

Explanation:

All the radioactive reactions follow first order kinetics.

The equation used to calculate rate constant from given half life for first order kinetics:

We are given:

Putting values in above equation, we get:

The equation used to calculate time period follows:

where,

= initial mass of sample X = 78 g

N = remaining mass of sample X = ? g

t = time = 16.5 min

k = rate constant =

Putting values in above equation, we get:

Hence, the remaining amount of sample X is 6.9 g

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