**Decomposition of Limestone by HCl Acid**

Limestone is a sedimentary rock primarily composed of calcium carbonate (CaCO3). It can be decomposed by hydrochloric acid (HCl) to produce calcium chloride (CaCl2), carbon dioxide (CO2), and water (H2O). In this question, we need to determine the mass of HCl acid required to decompose 50g of limestone.

**Step 1: Determine the molar mass of CaCO3**

Calcium carbonate (CaCO3) has a molar mass of 40.08 g/mol (Ca) + 12.01 g/mol (C) + (3 x 16.00 g/mol) (O) = 100.09 g/mol.

**Step 2: Calculate the number of moles of CaCO3**

To calculate the number of moles of CaCO3, we divide the given mass (50g) by the molar mass of CaCO3:

Number of moles = Mass / Molar mass
Number of moles = 50g / 100.09 g/mol
Number of moles = 0.4998 mol (approximately)

**Step 3: Write and balance the chemical equation**

The balanced chemical equation for the reaction between HCl and CaCO3 is as follows:

CaCO3 + 2HCl → CaCl2 + CO2 + H2O

According to the balanced equation, 1 mole of CaCO3 reacts with 2 moles of HCl.

**Step 4: Calculate the number of moles of HCl**

Since 1 mole of CaCO3 reacts with 2 moles of HCl, the number of moles of HCl required can be calculated as follows:

Number of moles of HCl = 2 x Number of moles of CaCO3
Number of moles of HCl = 2 x 0.4998 mol
Number of moles of HCl = 0.9996 mol (approximately)

**Step 5: Calculate the mass of HCl**

Finally, to determine the mass of HCl required, we multiply the number of moles of HCl by its molar mass. The molar mass of HCl is 1.008 g/mol (H) + 35.45 g/mol (Cl) = 36.46 g/mol.

Mass of HCl = Number of moles of HCl x Molar mass of HCl
Mass of HCl = 0.9996 mol x 36.46 g/mol
Mass of HCl = 36.44 g

Therefore, approximately 36.44 grams of HCl acid is required to decompose 50 grams of limestone.