Answer :
To calculate the mass of 1.55 microcuries of Cs-137, one must convert microcuries to the number of atoms and then use the molar mass of Cs-137. This requires the decay constant for Cs-137, which isn't provided, hence the mass cannot be directly calculated in this case.
The student asked for the mass of 1.55 microcuries of Cs-137. Cesium-137 is a radioactive isotope with a known mass number (A) of 137, which means one mole of Cs-137 has a mass of 137 grams. One mole also contains Avogadro's number of nuclei, which is 6.02 imes 10^{23}. To find the mass corresponding to a certain amount of radioactivity, we need to use the decay constant of the isotope and the definition of a curie, which is based on the disintegrations per second.
The calculation involves converting the radioactivity in microcuries to the number of atoms, then relating that to the molar mass. Unfortunately, without the decay constant for Cs-137, this cannot be done directly here. However, in another context, such as a provided decay constant, the mass would be calculated using the aforementioned constants along with the decay equation that relates mass, radioactivity, and time.
