no of slaves for one master

how many slaves can i able to configure for one master using Xbee S2B module

That is dependent on if they are Routers or End device. For End devices, you can poll the NC parameter to see how many End devices you can have.

For Routers, there have been no limiting factor set by Digi beyond the total number of 16 bit addresses.

If this is a simple Point to multi-point network, it would be better for you to use one of the Non Mesh based products such as the XBee 802.15.4 module.