Four substances, P, Q, R, and S, are tested as shown.  

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Test Substance R Dilute No reaction Gas given off which pops" with a lighted splint No reaction Gas given off which turns hydrochloric acid added limewater milky No reaction Gas given off which turns Dilute aqueous sodium No reaction No reaction hydroxide added and red litmus paper to bluc warmed gently What are P Q R and S ? P R S Mg Mg Mg Na2CO3 NaCl Na2CO3 NHC1 NazCO3 Mg NHCI NazCO3 NaCl A B NaCI NH,CI NHC1 D NaCl