Help with my physical science PLEASE!?

[wilbart]

3. Which molecule contains the smallest number of hydrogen atoms?
a) N2H4
b) Al(OH)3
c) (NH4)2SO4
d) NH4NO3
4. Which kind of reaction is shown below?
2H2O2 ? 2H2O + O2
a) synthesis reaction
b) decomposition reaction
c) single replacement reaction
d) double replacement reaction
5. Which is evidence that the reaction below is a redox reaction?
2Na + Cl2 ? 2NaCl
a) The sodium atom is a pure element as a reactant and becomes part of a compound.
b) Two different elements take part in the reaction.
c) Oxidation occurs to both elements in the reaction.
d) There are no ions in the equation.
6. Which does Not describe a physical change happening to water?
a) water evaporating in the sun
b) water reacting with nitrogen gas
c) water freezing and being broken apart with a knife
d) water heating up on a stove
7. Which is proof that in any synthesis reaction, a chemical change has occurred?
a) In a synthesis reaction, two reactants combine to form a new compound.
b) Many synthesis reactions involve a phase change.
c) In a synthesis reaction, oxygen is always converted to carbon dioxide.
d) All synthesis reactions are exothermic.
8. Which property of matter allows convection currents to form?
a) Fluids rise if they are less dense than the matter around them.
b) The molecules in solids do not vibrate very quickly.
c) Electromagnetic waves carry energy.
d) Liquids take the shape of their container.
9. A student places one end of an iron nail in a cup of boiling water. Eventually, the whole nail is hot. He says that the heat transferred through the nail by convection. Which of the following explains why his statement is incorrect?
a) There was no movement of matter within the nail.
b) The nail did not emit any light.
c) The water did not change phase.
d) Only gases can transfer heat by convection.
10. What must be true for any endothermic reaction?
a) The chemical bonds of the products have more energy than the chemical bonds of the reactants.
b) There are more products than there are reactants.
c) There must be a phase change from solid to liquid or from liquid to gas.
d) The reaction must take place in a sealed container held at constant volume.
11. A student performs the reaction shown below.
NaOH + HCl ? NaCl + H2O
She increases the concentrations of NaOH and HCl, and finds that NaCl is produced much more quickly. Which explains the outcome of her experiment?
a) NaOH and HCl molecules collide more frequently at higher concentrations.
b) NaCl requires a high concentration for any reaction to occur.
c) HCl acts a catalyst, but only at high concentrations.
d) The higher concentrations create a higher temperature in the solution.
12. A chemist has two compounds that do not chemically react. He thinks that by finding the right catalyst, he can get them to react. Why is the chemist incorrect?
a) Catalysts can only increase the rate of reaction for compounds that do react.
b) Only an inhibitor can cause two compounds to react.
c) The activation energy of the reaction is already zero.
d) A catalyst cannot increase the concentration of reactants.
13. Which would you most expect to be an unstable atom?
a) a carbon (C) atom with 6 protons and 6 neutrons
b) an iron (Fe) atom with 26 protons and 27 neutrons
c) a helium (He) atom with 2 protons and 2 neutrons
d) a curium (Cm) atom with 96 protons and 85 neutrons
14. Americium–241 decays into neptunium–237. Which correctly describes this process of radioactive decay?
a) An unstable nucleus decays into a more stable nucleus.
b) Energy in the nucleus is converted into mass.
c) The strong nuclear force splits the nucleus apart.
d) The atom loses four protons.
15. A scientist observes that the particles emitted by a radioactive substance cannot be detected when the substance is enclosed in a thin sheet of paper. He thinks that the sample is polonium (Po, atomic number 84) and that it is decaying to astatine (At, atomic number 85) by beta decay. Which statement correctly assesses his conclusion?
a) It could be this reaction, because nuclear fission does not release particles.
b) It could be this reaction, because alpha particles are blocked by the paper.
c) It cannot be this reaction, because beta particles would penetrate the paper.
d) It cannot be this reaction, because gamma rays are blocked by paper.
16. In the sun, hydrogen (H) nuclei (protons) combine to form helium (He) during nuclear fusion. The total mass of the He that is formed is less than the mass of the H atoms used and in the process, energy is released. Which statement explains the relationship between mass and energy in nuclear fusion?
a) Energy has been converted into mass.
b) Mass has been converted into energy.
C) Mass and energy have been created.
d) Mass and energy have been absorbed.