why is it necessary to subtract the value for water vaorp pressure from atomophere pressure to determine the pressure of H2 gas

? you expect us to answer this? ? this is your schoolwork, i don't think we can with this, i think it would considering being

warm front forms when a moist, warm air mass slides up and over a cold air mass. as the warm air mass rises, it condenses into a broad area of clouds. a warm front brings gentle rain or light snow, followed by warmer, milder weather.

hope i !