Im missing two and I could use help.

[Tom]

Which has more atoms: a 1-gram sample of carbon-12 or a 1-gram sample of carbon-13?

A) More information is needed.

B) They have the same number of atoms.

C) A one gram sample of carbon-13

D)* a one gram sample of carbon-12

 

What is the total number of protons and neutrons in a water molecule?

A) 10

B) 12

C) 15

D)* 18

E) none of these

 

Humidity is a measure of the amount of water vapor in the atmosphere. Why is humidity always very low inside your kitchen freezer?

A) because the frost in the freezer absorbs this moisture

B) because the kitchen freezer is most often sealed off from the atmosphere

C) because it is not possible for water to be in the gaseous phase at temperatures below 0°C

D)* At the cold temperatures of your kitchen freezer, water molecules in the vapor phase are moving relatively slowly, which makes it easier for them to stick to inner surfaces within the freezer or to other water molecules.

Edited May 22, 2009 by Tom
Found information helping with answer.

[D H]

Which two are you missing? You have one answer marked with an asterisk for each question. Are these your asterisks?

 

We do not do your homework for you here at Science Forums. Doing that would not help you learn. Instead, we help you to do your own homework. That means we need more input from you besides just restating your homework problems.

[Theophrastus]

My best guess is that the asterisks indicate his selected answers, and he's current calling upon (I know, overly dramatic:-)) the community for feedback. Is feedback and criticism, of mistakes as long as the correct answer isn't explicitly given, adequate?

Edited May 22, 2009 by Theophrastus
adding content (not that there's veryu much of it in the first place)

[Tom]

The * are my choices and Im just asking direction so I can answer these Questions.

[jdurg]

The * are my choices and Im just asking direction so I can answer these Questions.

 

Then what are your reasons for picking these answers? Once we see where you're coming from, we can provide more help.

[Fuzzwood]

The answers themselves are correct. Regardless of them being multiple choice, can you give your motivation for your answers?

[D H]

Are they? The last question in particular is awful. It is ambiguous: Absolute or relative humidity? The selected answer only looks at half of the picture, the vapor. None of the answers look at the whole picture (the frost and the gas), and none of the answers is anywhere close to correct if the question is asking about relative humidity.

 

Multiple guess questions. Yuck.

[Theophrastus]

Yeah, similarly in the second question, theoretically, you could make a water molecule, using different isotopes. For example hydrogen can at times have no neutrons, one neutron, or two. (or three) These can all alter the atomic mass.

The humidity question too is vague, as you pointed out D H, however, when I do multiple choice, I don't necessarily intend it to be the correct answer, but rather the answer that most closely fits the demands of the curriculum, and in all honesty, to have to think of testing in such a manner, really makes me question multiple choice,what with its fixed answers, and room to guess, and the ability to still attain credit for a guess, done at random.

Though, based on the expected curriculum, the answers all seem to be correct, yes, in spite of fallacies within the questions

[CaptainPanic]

Humidity is a measure of the amount of water vapor in the atmosphere. Why is humidity always very low inside your kitchen freezer?

A) because the frost in the freezer absorbs this moisture

B) because the kitchen freezer is most often sealed off from the atmosphere

C) because it is not possible for water to be in the gaseous phase at temperatures below 0°C

D) At the cold temperatures of your kitchen freezer, water molecules in the vapor phase are moving relatively slowly, which makes it easier for them to stick to inner surfaces within the freezer or to other water molecules.

E)* None of the above, but D comes closest.

The vapor pressure of water is low at low temperatures. This is indeed related to the velocity of water molecules in the gas phase. But explaining it as "easy" is a weird choice of words. And as pointed out earlier (by D H), we need to know whether we are discussing relative or absolute humidity.

 

I believe that the most widely used definition of "humidity" is in fact the relative humidity. Since there is ice present in (almost) every freezer, we might conclude that the gas phase in the freezer is in fact saturated with water. After being closed for a long time, it will be at equilibrium. The equilibrium state with ice present will be the saturated state, which means that there is in fact 100% (relative) humidity!! It's therefore very moist in a freezer, and it's impossible to evaporate sublimate any water.