65.5g of copper reacts with __g of oxygen to produce 81g copper(I) oxide

grams O₂(g) ≅ 15.9 g O₂(g) (3 sig. figs.)  

Explanation:

2Cu + O₂ => 2CuO

Convert given to moles, solve by equation rxn ratio then convert to grams.

Moles CuO formed = 81.0 g / 81.5 g·mol⁻¹ = 0.994 mol CuO

0.994 mol CuO requires 0.994 mol Cu = 0.994 mol Cu x 64 g·mol⁻¹ = 63.6 g Cu => from this, the amount of O₂ needed = 1/2(0.994 mol) O₂(g) = 0.497 mol O₂(g) = (0.497 mol O₂(g))(32 g·mol⁻¹) = 15.904 g O₂(g) ≅ 15.9 g O₂(g) (3 sig. figs.)                

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

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.