AX is a covalent diatomic molecule. The molecule is NO (Nitric oxide). Its bond order is 2.5 and it has a total of 15 electrons (7+8=15). Here ' A ' denotes nitrogen (N) and ' X ' denotes oxygen (O). NO is colourless and toxic gas. Note : Total number of electrons equal to 13 will also have the 2.5 bond order, but in this case neutral diatomic molecule will not be possible.