#### Answer

$39.7mg \space C_{21}H_{26}N_{2}S_{2}$ for one tablet

#### Work Step by Step

Let's use the entire 12 tablet data and divide by the answer by 12 to get the initial tablet thioridazine content
We are given $.301g$ BaSO$_{4}$ so we need to work backwards in the way the reaction occurred because we started with Thioridazine and ended with BaSO$_{4}$
$\frac{0.301g\space BaSO_{4}}{1}\times\frac{1 mol\space BaSO_{4}}{233.4g\space BaSO_{4}}\times\frac{1 mol\space SO_{4}^{-2}}{1 mol\space BaSO_{4}}\times\frac{1 mol\space C_{21}H_{26}N_{2}S_{2}}{1 mol\space SO_{4}^{-2}}\times\frac{370.2g\space C_{21}H_{26}N_{2}S_{2}}{1 mol\space C_{21}H_{26}N_{2}S_{2}}\times\frac{1000mg}{1g} = 477mg\space C_{21}H_{26}N_{2}S_{2} $
This mass is for 12 tablets so divide by 12 to get the mass for one tablet:
$477mg\space C_{21}H_{26}N_{2}S_{2} \div 12 = 39.7mg \space C_{21}H_{26}N_{2}S_{2}$