If a student measured an object’s density to be 2.70 g/mL, 2.32 g/mL, 2.12 g/mL and 3.88 g/mL then his results would considered The object’s actual density is 3.50 g/mL A. Accurate and precise

B. precise but not accurate

C. Neither accurate nor precise

D. Accurate but precise

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

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.