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The half-life (T_half) is the time it takes for the count rate (or activity) of a radioactive substance to reduce to half its initial value.Let's examine the data:At time = 0 s, count rate = 800 counts/s. Half of this is 400 counts/s.Looking at the table, the count rate drops from 480 counts/s (at 120 s) to 370 counts/s (at 180 s). The value of 400 counts/s falls between these two points. Thus, the half-life is between 120 s and 180 s.Let's check the options for the best estimate:If T_half = 120 s, then at 120 s, the count rate should be 800/2 = 400. The table shows 480. (Error: |480-400|=80)If T_half = 180 s, then at 180 s, the count rate should be 800/2 = 400. The table shows 370. (Error: |370-400|=30)Comparing the errors, the half-life of 180 s provides a closer estimate to the observed value at 180s than 120s does for 120s. Therefore, 180 seconds is the best estimate among the given options.