Tablet radiation (RF vs EMF ) I own a tablet without 3G/phone functionality but equipped with Wi-fi
There is a lot of mixing up RF (radio frequency) with EMF (electric magnetic field) when looking for health issues arising from radiation.

So :

if there is no 3G functionality, am I safe from RF ?

if there is Wifi then there should be RF too. If Wif-fi is enabled but not connected to a network, does it emit RF ?

EMF is another one, but a property of all electrically powered. In what case is it more emitted by the tablet ie when wi-fi is on ?

Which one is dangerous to health , RF or EMF RF vs EMF ? I see that there are cases that reduce radiation but all are concerned with RF and not EMF. Is there a solution that works for reducing EMF emission?
There's a lot of mixing up because the "aagh tinfoil hats" brigade are very mixed up themselves. There's no evidence that any radio emissions from mobile phones have any health effects whatsoever. You get a larger radio dose from your local TV transmitter than the phone in your pocket.

To answer your specific questions: yes, you're safe from RF if there's no 3G functionality, or if there is 3G functionality for that matter. If you turn on Wi-Fi, it emits radio waves (that's how it works!) regardless of whether it's connected to a network or scanning for networks.

As you say, EMF is just the "spill-off" from any electrical appliance or even cable. The EMF from tablets is almost too little to measure: it's several orders of magnitude less than from anything with an electric motor, such as a hairdryer or fan.

Neither RF nor EMF emissions from tablets or mobile phones are hazardous to health at all. A case to reduce the RF emissions is a bit pointless. Wi-Fi, Bluetooth, and 3G protocols all feature methods for the transmitter to change its transmission strength as necessary. Blocking the transmission just makes it transmit with more power, running your battery down faster.