I need guidance on connecting MQ-135,MQ-8,MQ-2 Gas Sensors with Arduino Mega and communicating to Android Mobile with Bluetooth hc-05.Need any source code and circuit block to build this application which senses harmful gases at same time at pushes to android app .App is developed already.
You might have put the cart before the horse but, as far as bluetooth is concerned, you need do no more than send the same data to Android that you would to the serial monitor, no extra programming required.
You might find the following background notes useful
http://homepages.ihug.com.au/~npyner/Arduino/GUIDE_2BT.pdf
http://homepages.ihug.com.au/~npyner/Arduino/BT_2_WAY.ino