The pairs of compounds which cannot exist together in aqueous solution are :<br>(I) NaH2PO4 and NaHC — s Block Elements Chemistry Question

💡 Solution & Explanation

Step 1: Analyze the chemical compatibility of the mixtures in solution. Compounds cannot co-exist if they undergo a neutralization reaction (acid-base reaction). Step 2: Pair I (NaH2PO4 and Na2HPO4) and Pair II (Na2CO3 and NaHCO3) are conjugate acid-base pairs that do not react with each other and can form stable buffer solutions. In contrast, Pair III (strong base NaOH and acidic salt NaH2PO4) and Pair IV (acidic bicarbonate NaHCO3 and strong base NaOH) will immediately react. Step 3: Since only pairs III and IV cannot exist together, the correct option is (b).