Consider the species CH4, NH4+ and BH4-. Choose the correct option with respect to these species:

🧠 Check whether all three species are isoelectronic (same number of electrons) and determine the geometry of each.

| Species | Electrons | Structure | Geometry | |---|---|---|---| | $\ce{CH4}$ | $6 + 4(1) = 10$ | 4 bonds + 0 LP | Tetrahedral | | $\ce{NH4+}$ | $7 + 4(1) - 1 = 10$ | 4 bonds + 0 LP | Tetrahedral | | $\ce{BH4-}$ | $5 + 4(1) + 1 = 10$ | 4 bonds + 0 LP | Tetrahedral |

All three have 10 electrons → isoelectronic. All three have 4 bond pairs and 0 lone pairs → all tetrahedral.

⚠️ Trap: Option (a) says "only two have tetrahedral structures" — incorrect since all three are tetrahedral. Option (c) says "only two are isoelectronic" — incorrect since all three have 10 electrons.

$\boxed{\text{Answer: (b) Isoelectronic and all have tetrahedral structures}}$