After 200 years, 9.84 grams of Cesium would remain.
Let N represent the amount of substance after t years
The half-life of a cesium is 30 years., hence, this can be represented by exponential function:

where a is the initial value and b is the multiplier.
There were initially 1000g of the substance
a) The exponential model for this situation is:

b) After 200 years (t = 200), the amount of Cesium remaining is:

Hence after 200 years, 9.84 grams of Cesium would remain
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