Which of the following statements is true?

boiling and melting points are chemical properties.
a molecule of oxygen can have atoms of carbon in it.
elements are substances made of only one type of atom.
the number of electron shells in an atom is called the atomic number.

What pressure will be exerted by 0.675 moles of a gas at 25*c if it is in a 0.750-l container?

Marcel just purchased 1.69 grams of iron fillings in order to make living putty for his 6 year old niece. how many moles of iron are made in his sample?

Achemistry student needs to standardize a fresh solution of sodium hydroxide. he carefully weighs out of oxalic acid , a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in of distilled water. the student then titrates the oxalic acid solution with his sodium hydroxide solution. when the titration reaches the equivalence point, the student finds he has used of sodium hydroxide solution. calculate the molarity of the student's sodium hydroxide solution. be sure your answer has the correct number of significant digits.