Agravitational field vector points toward the earth; an electric field vector points toward an electron. why do electric field vectors point away from protons? 1. protons have much larger mass. 2. unlike electrons, protons will produce an electric field of their own. 3. protons have more net charge than electrons. 4. protons are positively charged. 5. none of these

The correct answer is
 4. protons are positively charged. 

In fact, the direction of the electric field of a charged particle depends on the sign of the charge of the particle. While a negatively charged particle (such as the electron) produces an electric field that points toward the charge, a positively charged particle (like a proton) produces an electric field that points away from the charge. This can be proofed by using a positive test charge: if we put a positive test charge near a proton, this test charge will move away from the proton (because it is repelled from it, since they have same charge), and the direction of its motion gives the direction of the electric field generated by the proton, so away from it.