Explanation:

In a piconet, which is a network of Bluetooth devices, there can be one master device and multiple slave devices. The master device is responsible for establishing and controlling the piconet, while the slave devices communicate with the master.

The question states that in the piconet of Bluetooth, one master device can be a slave in another piconet. Let's break down the options to understand why option 'B' is the correct answer.

a) Can not be slave:
If a device is the master in a piconet, it means that it has control over the piconet and is responsible for managing the communication between all the devices within that piconet. As such, a master device cannot act as a slave device within the same piconet. Therefore, option 'a' is incorrect.

b) Can be slave in another piconet:
While a master device cannot be a slave in the same piconet, it can act as a slave in another piconet. Bluetooth devices can simultaneously participate in multiple piconets, allowing a master device from one piconet to be a slave device in another piconet. This flexibility allows for more complex network configurations and enables devices to communicate with each other even if they are part of different piconets. Therefore, option 'b' is correct.

c) Can be slave in the same piconet:
As mentioned earlier, a master device cannot be a slave in the same piconet. Therefore, option 'c' is incorrect.

d) None of the mentioned:
Option 'd' is incorrect because, as explained above, a master device can be a slave in another piconet.

In conclusion, the correct answer is option 'B' - a master device can be a slave in another piconet. This flexibility allows for more versatile and interconnected Bluetooth networks.