The given symptom picture – adapted to persons with dark hair and rigid fibre, weakly, psoric constitution with an excessively yellow, sallow complexion, and a predisposition to affections of the respiratory and urinary tracts – is characteristic of Causticum in homeopathic materia medica.
Let's briefly consider why the other options are less likely:
Lycopodium: Typically associated with persons who are intellectually keen but physically weak, with digestive issues, and often worse in the afternoon. They can have a sallow complexion but the other descriptors don't fit as closely.
Arsenicum album: Often suited to anxious, restless individuals who are worse at night and from cold, with burning pains and a tendency towards digestive disturbances. Their complexion might be pale or sallow, but the overall picture differs.
Sulphur: Known for individuals who are often warm-blooded, averse to bathing, with various skin complaints and a tendency towards catarrhal affections. Their complexion can be reddish or unhealthy-looking, but the specific combination of dark hair, rigid fibre, and yellow sallowness is less typical.
The combination of dark hair, rigid fibre, weakness, psoric diathesis, yellow sallow complexion, and susceptibility to respiratory and urinary tract issues strongly points towards the constitutional picture of Causticum.