What is the structure of 2-ethyl-3-hexyne?
Are you sure this is an hexyne, and not an heptyne?
Because this is an even-numbered acetylene, we could number from either end. The third and fourth carbon along the chain are triply bound.
Given this structure, we have defined the numbering system.
but this is not a valid name, because the longest chain is now 7 carbons long. Organic nomenclature insists that first you find the LONGEST hydrocarbyl chain. This is therefore an heptyne derivative.
Would you check your question?