Guild Wars 2

I feel that I don’t fully understand MF. Say I have 100% MF with all my gear. That means I have a 10% to pick up uncommon loot. But, does that mean that I pick up uncommon loot:
a. 1/10 of all enemies that I kill (probably not, but you never know)
b. 1/10 of all enemies that drop anything
c. 1/10 of all enemies that drop gear (weapons, armor or upgrades)
d. Something I haven’t thought of

Any response would be helpful

Everytime you kill a monster you roll on a number of tables, inside these tables are different rarity categories.
Magic find increases the chances you will get higher categories.
For example if there is a 1 in 10 category, and you have 200% magic find you will have 3/10 chances to get that category.
This improves not just the rarity of the items you get but can also improve your chances at getting trophies and rare crafting materials like lodestones.
^from wiki

But to answer the question, C is right i think. if a mob has uncommon stuff in it’s loot table you will have the extra 10% to get that loot. However if a mob is only tabled to drop junk, you will never get anything but junk.

I could be wrong tho :P

MF doesn’t improve your loot, it only gives a higher chance of getting the rarer loot. So yes, if a mob only has junk on its table, you will only get junk.

Wheter or not you get loot is independent from MF. Based on what I have read it depends on how much damage you do if this is above a enemy type specific threshold you get a roll on the loot table.
The loot tables (enemy specific) are divided in different categories ranging from junk to exotics (including pre-cursors) with no magic find chance you have a change of 1 in X to get items from a certain category where X is difference for each category. Having 100% MF will give you a chance of 2 in X (see http://wiki.guildwars2.com/wiki/Magic_find). Note that it is possible that loot tables may contain entries granting 2 or more items as a single row.
Based on this you MF increase the chance to get a higher category of loot after it has been (independently) decided that you will get loot. So I would say B is correct with a minor correction the percentage is not only dependent on your MF. As loot tables differ some tables may only contain junk or low level items so MF will not improve the rarity of these.