The products A and B obtained in the following reactions, respectively, are

3ROH + PCl₃ → 3RCl + A

ROH + PCl₅ → RCl + HCl + B

The correct answer is: H₃PO₃ and POCl₃

We are given two reactions involving an alcohol (ROH) reacting with phosphorus chlorides, and we need to identify the products A and B.

Reaction 1:
3ROH + PCl₃ → 3RCl + A

Let us balance and analyze this reaction. Phosphorus trichloride (PCl₃) reacts with three molecules of alcohol. In this reaction, each alcohol molecule donates its −OH group and receives a −Cl from PCl₃, producing the alkyl chloride (RCl).

Now, let's track the atoms to identify product A:
• Reactant side: 3 R atoms, 3 O atoms, 3 H atoms (from 3 ROH) + 1 P atom, 3 Cl atoms (from PCl₃)
• Product side (known): 3 R atoms, 3 Cl atoms (from 3 RCl)

The remaining atoms that must appear in product A are: 1 P, 3 O, and 3 H. This gives us the formula H₃PO₃, which is phosphorous acid (also written as P(OH)₃).

So, A = H₃PO₃

The complete balanced reaction is:
3ROH + PCl₃ → 3RCl + H₃PO₃

Reaction 2:
ROH + PCl₅ → RCl + HCl + B

Here, phosphorus pentachloride (PCl₅) reacts with one molecule of alcohol. The −OH group of the alcohol is replaced by −Cl, producing the alkyl chloride and HCl as by-products.

Let's track the atoms to identify product B:
• Reactant side: 1 R, 1 O, 1 H (from ROH) + 1 P, 5 Cl (from PCl₅)
• Product side (known): 1 R, 1 Cl (from RCl) + 1 H, 1 Cl (from HCl)

The remaining atoms for product B are: 1 P, 1 O, and 3 Cl. This gives us the formula POCl₃, which is phosphorus oxychloride (also called phosphoryl chloride).

So, B = POCl₃

The complete balanced reaction is:
ROH + PCl₅ → RCl + HCl + POCl₃

Summary:
• Product A (from the reaction of alcohol with PCl₃) = H₃PO₃ (Phosphorous acid)
• Product B (from the reaction of alcohol with PCl₅) = POCl₃ (Phosphorus oxychloride)

Therefore, the correct answer is H₃PO₃ and POCl₃.