I believe it is hydroxide(OH-)ions
H+ + OH- -->H2O
Hydrogen ions
Not simple to answer - acidic solutions contain more hydrogen ions that hydroxide ions, but there are very many ions that can cause hydrogen ions to be in excess - for instance the hydrogen-sulphate ion (from an acid salt such as sodium hydrogen-sulphate) when added to water has a tendancy to split into hydrogen and sulphate ions, so making the solution acidic. Not all acid salts are acid in soultion - for instance sodium hydrogen-carbonate is alkaline. When dissolved in water, the hydrogen-carbonate ion tends to react with hydrogen ions in the water to form molecular carbonic acid - removing hydrogen ions from the water and hence making it alkaline. Acid salts of strong acids, such as sulphuric, hydrochloric, nitric, are acidic in solution. Acid salts of weak acids, such as carbonic, sulphurous, are alkaline in solution. Just a few simple examples.
The simple answer is H+ ions (hydrogen ions). Because the element hydrogen is made up of a proton an an electron, a positive hydrogen ion is just a proton. The two theories of acid-base are the 'Arrenhius Theory' and the 'Bronsted-Lowry Theory'. Arrenhius theory says that an acid is a substance which produce hydrogen ions in solution. The Bronsted-Lowry theory says that an acid is a proton donor. This is a huge topic in physical chemistry and this is just a basic explanation of what an acid is. There are strong acids and weak acids, strong bases and weak bases etc.
This is because metals have positive ions and so does hydrogen. Hence the nature of their reactivity is same but the value of reactivity is different. Therefore metals replace hydrogen in a reaction while non metals dont...
In water, which is a polar molecule, ions care surounded by water molecules depending on the charge of the ion. Positive ions form eletrostatic interactions with the oxygen in water and negative ions, with the hydrogens. Polar molecules are easily dissolved in water because they form hydrogen bonds, sort of the same principle behind the interactions that happen between ions and water molecules.
Bases combines easily with hydrogen atoms
A base
Acids. They dissociate in water/aqueous solutions to from hydrogen ions (and the corresponding anion).
Why water, of course, just through in the electrons needed.
Buffer
The Arrhenius acids give proton or hydrogen ion or hydronium ion in water.
Acids release hydrogen+ ions (H+) when dissolved in water
Acids dissolve in water to release hydrogen ions.
the difference is that ,the hydrogen ion
ACIDS form hydrogen ions H+ in water. Bases form hydroxide ions OH-in water
acids give off H+ ions
Because the number of positive hydrogen ions produced is equal to the number of negative ions produced, water is neutral. Water is neutral despite the production of hydrogen ions and hydroxide ions because the number of positive hydrogen ions produced is equal to the number of negative ions produced, water is neutral.