how many sensor integrating on wifi module

How many sensors one aurdino mega support can support with wi-fi modules??

would it b best to use zigbee,wifi or bluetooth module for data transfer??

How much data do you want to transfer, and at what rate (bytes per second)? How far do you want to transfer it? What will it come from? What will it go to?

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What sort of sensors have you got that connect using WiFi ?

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ECG ,EEG,BP sensors with wi-fi modules.

I want to trasnfer data upto 10 meter ,from sensors employing on body(ECG,EEG,PB sensors) . n it will go to aurdino board the from there it will go to gateway (smart phone)

ECG ,EEG,BP sensors with wi-fi modules.

Each of the sensors has a WiFi shield?

Or are they connected to one Arduino which is wearing a WiFi shield?

The number of sensors that can be attached to an Arduino is limited by the number of available pins. The WiFi shield uses a few pins. The rest can have sensors attached to them.

I want to trasnfer data upto 10 meter

Then XBee or bluetooth makes sense. If you use bluetooth, though, you need an Arduino with bluetooth at each place that the sensors will be. If you use XBee, you can connect the sensors directly to the XBee.

Having several XBees talk to one XBee is far easier than having several bluetooth devices talking to a bluetooth device. The term pairing means two.

Getting from the receiver end to the phone is a completely separate issue.