blz explain this the given answer was 6 Out of following how

Last updated: 7/4/2023

blz explain this the given answer was 6 Out of following how many mixtures are buffers solution i NaCN 0 5 mole ii NaCN 0 5 moles HCN 0 5 moles iii NH3 1 mole NH4Cl 1 mole iv CH3COOH 1 mole NaOH 0 75 moles v NH4Cl 1 mole NaOH 0 75 moles vi CH3COONa 0 5 moles HCI 0 25 mole vii H CO3 1 mole NaOH 1 5 moles