So far there have only been 6 named Mega Stones: Lucarionite, Blazikenite, Mewtwonite X, Mewtwonite Y, Charizardite X, and Charizardite Y. Lucarionite is the only one listed prior that can be obtained through normal gameplay in both games. Blazikenite must be obtained through an event, which begins on October 12 and lasts until January 15, 2014. Mewtwonite X and Charizardite X can be obtained only in Pokemon X, and Mewtwonite Y and Charizardite Y can only be obtained in Pokemon Y. Mega Stones can be traded between these two games.
In Pokemon X and Y you are not allowed to sell mega stones unfortunately. They are considered a special item.
You cannot find the Mega Stone for Latios in Pokémon X or Pokémon Y.
There is no such thing as a mega stone in Pokémon Pearl. Mega stones were first introduced in Pokémon X and Y and are required for certain Pokémon to Mega Evolve, which is a temporary new evolution stage.
The Mewtwonite X is exclusively for Pokémon X while the Mewtwonite Y is exclusively for Pokémon Y, so in order to get both Mega Stones (or more of the same one) and another Mewtwo in a single game, trading is required.
No, because Mega Evolution wasn't introduced until Pokemon X and Y.
Mewtwo can Mega Evolve into either Mega Mewtwo Y or Mega Mewtwo X.
Nowhere. As of now there is no such a thing as a Mega Salamence.
Good physical sweepers in Pokemon X and Y are Mega Lucario, Mega Mawile, and Heracross. Other good special sweepers in Pokemon X and Y are Manectric, Alakazam, and Mega Gengar.
Mega Charizard X, which is exclusively for Pokémon X, is a Fire/Dragon-type Pokémon, while Mega Charizard Y is Fire/Flying (Pokémon Y only).Its respective Mega Stone is acquired as soon you pick Charmander from Professor Sycamore.
Pokémon exclusive to X version include-Mega Charizard XMega Mewtwo XStaryuStarmieHoundourHoundoomPoochyenaMightyenaAronLaironAggronLileepCradilyAnorithArmaldoSawkSwirlixSlurpuffClauncherClawtizerXerneas
Mewtwo is the ultimate Psychic type legendary Pokemon. It was introduced in the first generation and does not evolve into any other Pokemon, although as of the sixth generation it can mega evolve into Mega Mewtwo X or Mega Mewtwo Y.
This depends if you are referring to Mega Charizard X or Mega Charizard Y. Mega Charizard X is black and blue with darker blue wings. Mega Charizard Y has similar coloring to regular Charizard and is orange and yellow with turquoise wings.