नीचे दो कथन दिए गए हैं : एक को अभिकथन A और दूसरे को कारण R के रूप में लेबल किया गया है। अभिकथन A: \( O \) की प्रथम आयनन एन्थैल्पी \( N \) और \( F \) से कम होती है। कारण R: \( O \) से एक इलेक्ट्रॉन का नुकसान स्थिर अर्ध-पूर्ण \( p \) कक्षक की ओर ले जाता है। उपरोक्त कथनों के प्रकाश में, नीचे दिए गए विकल्पों में से सबसे उपयुक्त उत्तर चुनिए:

First ionization enthalpy of \( O \) is indeed lower than \( N \) (due to stable half-filled \( 2p^3 \) in \( N \)) and \( F \) (due to higher nuclear charge in \( F \)). However, losing an electron from \( O \) (\( 2p^4 \to 2p^3 \)) leads to a stable half-filled \( p \) orbital, making ionization easier, but Reason states 'loss of electron leads to stable half-filled p orbital', wait, the reason is correct for why \( O \) has lower IE than expected or relatively low, but let's check: loss of electron from \( O \) gives \( O^+ \)(\( 2p^3 \)), which is stable half-filled, so Reason is correct and is the explanation. Wait! Let's check option 3: \( A \) is correct but \( R \) is not correct. Wait, \( O \) has \( 2p^4 \). Removing one electron gives \( 2p^3 \) (half-filled, extra stability). Thus, the energy required is lower. So \( R \) is correct and explains \( A \). Wait, why would option 3 be correct? Let's check answer key: \( A \) is correct, but \( R \) says 'loss of electron from O leads to stable half-filled p orbital', which is true!