Step 1:

A solution made by mixing 0.10 mol of HCN  with 0.040 mol NaOH in 1.0 L of aqueous solution.

List the major species involved in reaction are HCN, Na⁺, OH^–, H₂O.

Note : Here NaOH is not a major species.

To have the clear idea consider the possibilities for the dominant reaction are

H₂O(l) + H₂O(l) H₃O+(aq) + OH–(aq)

HCN(aq) + H₂O(l) H₃O+(aq) + CN–(aq)

HCN(aq) + OH–(aq) CN–(aq) + H₂O(l)

Na+(aq) + OH–(aq) NaOH

Na+(aq) + H₂O(l) NaOH + H+(aq)

Solution:

Major species involved in reaction are HCN, Na⁺, OH^–, H₂O.