Refer to figure. 
EASA learning objective 022.05.02.01.03 says: 'State that in-flight realignment is not possible and loss of alignment leads to loss of navigational data although attitude information may still be available.'
EASA learning objective 022.05.02.01.09 states: ‘Explain the following selections on the IRU mode selector: NAV (normal operation); ATT (attitude only).’

Switching an IRS off in the air will lead to loss of alignment which means the loss of all navigational data. In flight realignment isn't possible as an IRS needs to be stationary on the ground for alignment to take place.

Selecting 'ATT' during 30 seconds of straight and level unaccelerated flight will allow the IRS to produce attitude information and, when synchronised with another source, heading information but re-selecting NAV will not produce anything of use! Bear in mind that modern civil air transport aircraft carry a minimum of 2 IRS so you'll always have a back up.

Attiude information can be recovered in flight → CORRECT. Selecting 'ATT' during 30 seconds of straight and level unaccelerated flight will allow the IRS to produce attitude information.

Depending on aircraft type realignment may not be possible in the air → INCORRECT.  LO 022.05.02.01.03 says: ‘State that in-flight realignment is not possible and loss of alignment leads to loss of navigational data although attitude information may still be available.’ Real world technology advances make this possible on some aircraft but the exam is based on the LO so the ‘Depending on aircraft type…’ ststement makes this statement incorrect.

The IRS can be realigned by transferring information from another IRS → INCORRECT.  No it can't see above!

Switching to NAV will regain all navigation functions → INCORRECT.  No it won't, alignment is lost and it cannot be realigned in flight.