Final answer:
In B+ decay, the exchange particle is a positron (B+), which is emitted when a proton in the nucleus is converted into a neutron and a neutrino via the weak nuclear force.
Step-by-step explanation:
The exchange particle involved in B+ decay, also known as positron emission, is the positron (B+), which is the antimatter counterpart of the electron. In B+ decay, a proton within the nucleus is transformed into a neutron, a positron, and a neutrino, conserving the total electric charge. This decay process is a manifestation of the weak nuclear force and is an example of the conservation of the total number of nucleons and electron family number. After the positron is emitted, it will typically find an electron and annihilate, producing gamma rays in the process.