Answer:
The formula used for titrations has general application for complete reactions and can be used here . However, a direct chemical thinking is even simpler. 15 ml of a 0.21M NaOH solution contain 15X0.21 mEq ( milliequivalents, see referenced answer above) of NaOH and by definition require the same number of equivalents to react completely with the unknown compound( X ) . Therefore : Eq (X) = 25/0.21 x 15 = 7.95g
Step-by-step explanation: