Final answer:
At STP, one mole of gas occupies 22.4 liters. To find the number of moles in 0.77 liters of Br at STP, divide the volume by the molar volume at STP, resulting in approximately 0.03 moles which corresponds to option A in the multiple-choice answers.
Step-by-step explanation:
The question asks how many moles are in 0.77 liters of Br at STP. At STP (Standard Temperature and Pressure), one mole of any gas occupies 22.4 liters of volume. To answer the question, we can use the following calculation:
Number of moles = Volume of gas at STP / Volume occupied by 1 mole at STP
= 0.77 L / 22.4 L/mol
Therefore, the number of moles of Br in 0.77 liters at STP is approximately 0.034375 moles. When looking at the given options, the closest value is 0.03 moles, so the answer would be option A.