In h3po4 , 3 H atoms are present and in cahpo4 , 1 H atom is there so we can say that it donate 2 H atom
h3po4 ----->hpo4^-2 + 2H+
so valency factor is 2 . eq wt= mol. wt /v.f = 98/2 =49

To determine the equivalent mass of H3PO4 in the given reaction, we need to understand the concept of equivalent mass and stoichiometry.

**Equivalent Mass:**
The equivalent mass of a substance is defined as the mass of the substance that can combine with or replace 1 gram equivalent of hydrogen or any other element. The equivalent mass is calculated by dividing the molar mass of the substance by the number of equivalents.

**Stoichiometry:**
Stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction. It helps us determine the amount of substances involved in a reaction based on their stoichiometric coefficients.

Now let's analyze the given reaction:

Ca(OH)2 + H3PO4 → CaHPO4 + 2H2O

From the balanced equation, we can see that 1 mole of H3PO4 reacts with 1 mole of Ca(OH)2 to form 1 mole of CaHPO4 and 2 moles of H2O.

Since the reaction involves 1 mole of H3PO4, we need to calculate the equivalent mass of H3PO4.

**Calculating the Equivalent Mass:**

1. Determine the molar mass of H3PO4:
H = 1.01 g/mol (1 hydrogen atom)
P = 30.97 g/mol (1 phosphorus atom)
O = 16.00 g/mol (4 oxygen atoms)
Total molar mass = (3 * 1.01) + 30.97 + (4 * 16.00) = 98.00 g/mol

2. Calculate the number of equivalents:
Since 1 mole of H3PO4 reacts, it is equivalent to 1 equivalent.

3. Divide the molar mass by the number of equivalents to obtain the equivalent mass:
Equivalent mass = Molar mass / Number of equivalents
= 98.00 g/mol / 1 equivalent
= 98.00 g/equivalent

Therefore, the equivalent mass of H3PO4 in the given reaction is 98.00 g/equivalent.

**Answer Explanation:**

The correct answer is (D) 49 g/mol because we need to consider the molecular formula of H3PO4, which implies there are 3 hydrogen atoms in each molecule of H3PO4. Thus, the equivalent mass is calculated by dividing the molar mass (98.00 g/mol) by the number of equivalents (3). Therefore, the equivalent mass of H3PO4 is 98.00 g/mol / 3 = 32.67 g/equivalent. Rounding it to the nearest whole number, we get 33 g/equivalent, which is closest to option (D) 49 g/equivalent.