The chemical formula for the product is RbBr.
Answer : The correct option is (3) 500 K and 0.1 atm.
Explanation :
A real gas behaves ideally at high temperature and low pressure.
The ideal gas equation is,

where,
P = pressure of gas
V = Volume of gas
R = Gas constant
T = temperature of gas
n = number of moles of gas
The ideal gas works properly when the inter-molecular interactions between the gas molecules and volume of gas molecule will be negligible. This is possible when pressure is low and temperature is high.
Therefore, the correct option is (3) 500 K and 0.1 atm.
The empirical formula of the compound is calculated as follows
first calculate the mass of oxygen= 12-(4.09 +3.71)= 5.02g
then calculate the moles of each element, moles = mass/ molar mass
moles of K = 4.09g/39 g/mol(molar mass of K) = 0.105 moles
moles of Cl = 3.71g/35.5 g/mol(molar mass of Cl) = 0.105 moles
moles of O = 5.02g/ 16g/mol(molar mass of O) = 0.314 moles
then calculate e mole ratio by dividing each mole by the smallest number of moles ( 0.105 moles)
K=0.105/0.105= 1
Cl=0.105 /0.105=1
O= 0.314/0.105=3
therefore the empirical formula = KClO3
The concentration of hydrogen can be shown as:
[H+ ] = 3 * 10-5 M
pH can be determined as:
pH = - log [H+ ]
= - log (3 * 10-5)
= 4.53
Thus the pH of solution is 4.53