Here's how to determine the number of valence electrons in the methane diazonium ion (CH3N2+):

1. Identify the atoms and their valence electrons:

* Carbon (C): 4 valence electrons

* Hydrogen (H): 1 valence electron

* Nitrogen (N): 5 valence electrons

2. Account for the positive charge:

* The positive charge indicates the loss of one electron.

3. Calculate the total valence electrons:

* Carbon: 4

* Hydrogen (3 atoms): 3 * 1 = 3

* Nitrogen (2 atoms): 2 * 5 = 10

* Total: 4 + 3 + 10 = 17

* Subtract 1 electron for the positive charge: 17 - 1 = 16

Therefore, the methane diazonium ion (CH3N2+) has 16 valence electrons.