Near the earth surface, _______ air rises up and ________ air comes down.

Answer

C

Explanation

Hint : `t = 2.303//k log [R]_0//[R]`
`[R] = 10 g and [R]_0 = 20 g `
`t = 2.303//k log 2 implies 2.303 xx 0.3010//0.01 `