If the volume of a gas was measured to be 1.5L with the initial pressure unknown. After the volume increased to 3.5L, the pressure was measured to be 1.3atm. What was the initial pressure?

We can't until we know what we are working with or on

According to arrhenius theory of acid and bases, an acid is a proton donor, while base donates hydroxyl ions. further, acid and base reacts to form salt and water.consider following example.hcl    +      h2o          →      cl-          +      h3o+here, hcl has donated a proton, hence it is an acid.now consider following reactionhcl      +      naoh            ↔      nacl      +        h2oin this reaction, hcl donates proton, hence it is acid. on other hand, naoh donates hydroxyl ion (i.e. hence it is a base.