Hi, I need help with this...

a) I know that LANS are Large Area Networks... But why do LANS have distance limitations

b) What is the difference between the IEEE 802.2, 802.3, and 802.5 standards?

Learn to use Google.

A - Local Area Network - distance is limited by the carrier medium such as copper cable or fiber - The mostly used Ethernet cable standards and Specifications | NetworkDictionary (http://www.networkdictionary.com/networking/EthernetCableStandardsSpecifications.php)

B - LMSC, LAN/MAN Standards Committee (Project 802) (http://www.ieee802.org/)