The textbook traces the origin of commercial radio advertising to a specific event: “In 1922, a station in New York ran a 10-minute talk on the merits of some co-op apartments in Jackson Heights, N.Y. — and charged $50 for their effort. That was deemed a toll broadcast — now better known as a commercial.” The textbook later identifies this as station WEAF, New York on August 28, 1922, for the Queens Boro real estate corporation, voiced by H.M. Blackwell. This single broadcast established the principle that radio time could be sold to advertisers to reach audiences — creating the commercial broadcast model that would define American radio (and later television) for decades. This contrasts sharply with the BBC's licence-fee model (public funding) established in Britain in 1923, which sought to keep radio independent of commercial pressures.

First, calculate the volume of nitrogen at STP ($P_1V_1/T_1 = P_2V_2/T_2$):

• $P_1 = 715 - 15 = 700 \text{ mm Hg}$ [cite: 3, 53]
• $V_1 = 50 \text{ mL}$, $T_1 = 300 \text{ K}$ [cite: 18]
• $V_{STP} = \frac{700 \times 50 \times 273}{300 \times 760} \approx 41.9 \text{ mL}$ [cite: 19]
• Mass of $N_2 = \frac{28 \times 41.9}{22400} \approx 0.0524 \text{ g}$ [cite: 54]
• $\% \text{ Nitrogen} = \frac{0.0524}{0.3} \times 100 \approx 17.46\%$ [cite: 56]