If the half-life of a sample of a radioactive substance is 30 seconds, how much would be left after 60 seconds? a. one-fourth b. half c. one-eighth d. you would need to know how many atoms you are starting with.

Complete the sentence. the lower the hydrogen ion concentration, the the ph. higher lower closer to 7 closer to 0

)benzene and toluene form nearly ideal solutions. consider an equimolar solution of benzene and toluene. at 20 °c the vapour pressures of pure benzene and toluene are 9.9 kpa and 2.9 kpa, respectively. the solution is boiled by reducing the external pressure below the vapour pressure. calculate (i) the pressure when boiling begins, (ii) the composition of each component in the vapour, and (iii) the vapour pressure when only a few drops of liquid remain. assume that the rate of vaporization is low enough for the temperature to remain constant at 20 °c.

Oil rich countries in the middle east cover about 4% of earths total land area but prossess about 48% of the worlds known oil reserves what is the main reason for high concentration of reserves in this part of the world