Element a has seven valence electrons. how does its reactivity compare to that of element b, which has four valence electrons? element a is more reactive. element a is less reactive. element a and b have the same reactivity. element a has no reactivity

Sum of brother and sisters age is 26. four times the brothers age is subtracted from three times the sisters age, the difference is 8. what are the ages of the brother and sister?

Butane gas reacts with oxygen gas to give carbon dioxide gas and water vapor (gas). if you mix butane and oxygen in the correct stoichiometric ratio, and if the total pressure of the mixture is 390 mmhg, what is the pressure (in mmhg) of water vapor after the reaction is completed (temperature and volume do not change).

Sandy is building a small toy car. he wants to use a balloon to power the toy car. he fills a balloon with air and then attaches a straw to the balloon. he tapes the balloon-straw combination to the car and then releases the end of the balloon. the toy moves forward as the air from the balloon comes out the back of the straw. what can sandy do to make the toy car move faster? a) use less air in the balloon. b) blow up the balloon more. c) use a longer straw. d) use larger tires.