A 90-m3 basement in a residence is found to be contaminated with radon coming from the ground through the floor drains. The concentration of radon in the room is 1.5 Bq/L under steady-state conditions. The room behaves as a CSTR and the decay of radon is a first-order reaction with a decay rate constant of 2.09 3 1026 s21 . If the source of radon is closed off and the room is vented with radon-free air at a rate of 0.14 m3 /s, how long will it take to lower the radon concentration to an acceptable level of 0.15 Bq/L

25 minutes

Explanation:

V = Volume =

= Radon concentration under steady state = 1.5 Bq/L

k = Radon decay rate =

= Venting rate =

= Final concentration of radon = 0.15 Bq/L

Theoretical detention time is given by

We have the relation

The time taken to reach the acceptable level of concentration is 25 minutes.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.