Zaydun qāʾimun is nominal. In أَزَيْدٌ قَائِمٌ؟ the hamza asks a question without changing the case of mubtadaʾ or khabar.
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Nominal Sentence
The Two Interrogative Particles: Hamza and Hal
Zaydun qāʾimun is nominal. In أَزَيْدٌ قَائِمٌ؟ the hamza asks a question without changing the case of mubtadaʾ or khabar.