which is more basic?

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I believe the 1st one is more stable as CH3 is a slight donating group. A slight donating group would make the negative charge on the oxygen slightly less stable, so having less donating groups makes it more stable...at least in my mind.

A more stable base = a stronger acid = a weaker base. This would make the 2nd one a slightly stronger base. Hope that I am right, take this with a huge lump of salt as I am going off the top of my head and did not look it up.
 
Second one - the butanoate ion is more basic because it has 4 carbons as oppose to the first one - propanoate ion. Carbons are electron donation groups, and therefore increase basicity. Electron withdrawing groups will decrease basicity. Hope this helps.
 
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