Some elements are more reactive than other elements why do you think this is

Different elements all have different amounts of electrons in there outter shell.

Explanation

If you look at a periodic table, the elements are all listed in "Groups" up at the top you'll see the numbers, or columns. Each column's number represent how many electrons there are in each particular element.

hope this makes sense

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide