An airplane began with an initial velocity of 120 m/s and ended with a final velocity of 180 m/s in 4 seconds. What was its acceleration? A.60 m/s/s
B.15 m/s/s
C.45 m/s/s
D.30 m/s/s

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.

nuclear fission produces elements that are heavier than helium.

the elements that are used in nuclear fission and their products are much heavier than helium.