CC2650EM-5XD-RD: channel used in zigbee communication?

#if !defined( ZNWK_DEFAULT_CHANLIST )
/**
* Maximum Channel List - all channels
*/
#define ZSTART_MAX_CHANNELS_24GHZ 0x07FFF800
/**
* Default channel is Channel 11 - 0x0B
* Channels are defined in the following:
* 0 : 868 MHz 0x00000001
* 1 - 10 : 915 MHz 0x000007FE
* 11 - 26 : 2.4 GHz 0x07FFF800
*/
//#define ZNWK_DEFAULT_CHANLIST 0x04000000 // 26 - 0x1A
//#define ZNWK_DEFAULT_CHANLIST 0x02000000 // 25 - 0x19
//#define ZNWK_DEFAULT_CHANLIST 0x01000000 // 24 - 0x18
//#define ZNWK_DEFAULT_CHANLIST 0x00800000 // 23 - 0x17
//#define ZNWK_DEFAULT_CHANLIST 0x00400000 // 22 - 0x16
//#define ZNWK_DEFAULT_CHANLIST 0x00200000 // 21 - 0x15
//#define ZNWK_DEFAULT_CHANLIST 0x00100000 // 20 - 0x14
//#define ZNWK_DEFAULT_CHANLIST 0x00080000 // 19 - 0x13
//#define ZNWK_DEFAULT_CHANLIST 0x00040000 // 18 - 0x12
//#define ZNWK_DEFAULT_CHANLIST 0x00020000 // 17 - 0x11
//#define ZNWK_DEFAULT_CHANLIST 0x00010000 // 16 - 0x10
//#define ZNWK_DEFAULT_CHANLIST 0x00008000 // 15 - 0x0F
//#define ZNWK_DEFAULT_CHANLIST 0x00004000 // 14 - 0x0E
//#define ZNWK_DEFAULT_CHANLIST 0x00002000 // 13 - 0x0D
//#define ZNWK_DEFAULT_CHANLIST 0x00001000 // 12 - 0x0C
#define ZNWK_DEFAULT_CHANLIST 0x00000800 // 11 - 0x0B
//#define ZNWK_DEFAULT_CHANLIST ZSTART_MAX_CHANNELS_24GHZ
#endif // ZNWK_DEFAULT_CHANLIST

here also only channel 11 is enabled

Yes.

what is the advantages of using multiple channel instead of using single channel

You don't know ZC uses which channel so you must enable all of the channels for device to scan where the Zigbee network channel is.

u mean to say ...channel allocation in coordinator is dynamic?

If you enable all channels, ZC would pick one to form Zigbee network from scratch.

ok ..but which method is more efficient and reliable 1) using all channel or 2) using single channel

If you don't care about interoperability with Zigbee devices from 3rd parth, it's single channel more efficient and it's nothing to do with reliability.

so the channel is configured from f8wconfig.cfg file or it is also configured in other file in case of router ,ZNP(COORDINATOR) AND GATEWAY?

if want to hardcode the channel then where should i configure for znp and gateway

I would suggest you to do it from GW.