"Who is the eldest?"
Translation:Pwy yw'r hyna?
Older = henach, oldest = hyna(f)?
or are hynach and/or hena(f) also acceptable?
The two possible patterns (with the less common in brackets) here are :- (older/elder) = 'hŷn' '(henach') ; (oldest/eldest) 'hyna(f)' (hena(f)).
Maybe I'm missing something obvious, but could you translate 'who is the eldest' as 'pwy sy'n y hyna?' I offered that as an option but it wasn't accepted.
- Pwy sy'n hen? - Who is old?
When it could be anybody. But we ask
- Pwy ydy'r hynaf - Who is the eldest?
Because it will be a specific individual
- Pwy sy'n athro cemeg? - Who is a chemistry teacher?
- Pwy ydy'r athro cemeg? Mae'r labordy ar dân! - Who is the chemistry teacher? The lab is on fire!