The maximum number of molecules varies depending on the given conditions. Let's analyze each scenario to determine the maximum number of molecules present.

1) 15 L of water at STP:
At STP (Standard Temperature and Pressure), the temperature is 273.15 K (0°C) and the pressure is 1 atm. The molar volume of any ideal gas at STP is 22.4 L/mol. However, water is not an ideal gas, so we need to consider its density.

The density of water at STP is approximately 1 g/cm³. We can convert the given volume of 15 L to grams using the density:

Density = Mass / Volume
1 g/cm³ = Mass / 1000 cm³
Mass = 1000 g

Now, we need to convert the mass of water to moles using the molar mass of water (H₂O), which is approximately 18 g/mol. Therefore:

Moles = Mass / Molar mass
Moles = 1000 g / 18 g/mol
Moles ≈ 55.56 mol

Since 1 mole of any substance contains 6.022 x 10²³ molecules (Avogadro's number), we can calculate the maximum number of molecules:

Number of molecules = Moles x Avogadro's number
Number of molecules = 55.56 mol x 6.022 x 10²³ molecules/mol
Number of molecules ≈ 3.34 x 10²⁵ molecules

2) 15 L of H₂O gas at STP:
In this scenario, the given volume is already in gas form, so we don't need to consider the density. We can directly use the molar volume of an ideal gas at STP, which is 22.4 L/mol.

Moles = Volume / Molar volume
Moles = 15 L / 22.4 L/mol
Moles ≈ 0.67 mol

Number of molecules = Moles x Avogadro's number
Number of molecules = 0.67 mol x 6.022 x 10²³ molecules/mol
Number of molecules ≈ 4.03 x 10²³ molecules

3) 15 gm of ice:
In this scenario, we are given the mass of ice. To determine the number of molecules, we need to convert the mass of ice to moles using the molar mass of water (H₂O).

Moles = Mass / Molar mass
Moles = 15 g / 18 g/mol
Moles ≈ 0.83 mol

Number of molecules = Moles x Avogadro's number
Number of molecules = 0.83 mol x 6.022 x 10²³ molecules/mol
Number of molecules ≈ 4.99 x 10²³ molecules

4) Same in all:
The answer given is 1, which is incorrect. The maximum number of molecules is different in each scenario due to the different states of water (liquid and gas) and the given mass of ice.

In summary, the correct answer is:
1) 15 L of water at STP: Approximately 3.34 x 10²⁵ molecules.
2) 15 L of H₂O gas at STP: Approximately 4.03 x 10²³ molecules.
3) 15 gm of