No. The Lg 840g does not run the Android OS, which is required to install apps from Google Play.
The LG X145, also called the LG L60, is a tablet from LG that uses Android OS.
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Considering that you are asking about getting stock ROM of Android for LG devices, you can get it over the official website of LG.
Their first Android phone was the LG InTouchMax. They also have the LG Optimus line, for which they have both Android and Windows phones. Their latest is the LG Prada.
No
Yes, it does have the android market.
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No it is not possible to install android in java mobile. Its hardware is not compatible with android and also it does not enough memory to install android.
Nope - it runs on a very limited O.S type designed by LG - most probably you won't be able to install anything more than java applications.
You can find an in-depth tutorial on how to root an LG volt android phone on rootmyandroid.org/root-lg-volt-pc-safest-method.html
Yes. The LG Optimus series are Android smart phones currently running Android 2.2 Froyo and is scheduled to be upgraded to Android 2.3 Gingerbread.