A helium-filled balloon has a volume of 2.75 L at 20.°C. The volume of the
balloon decreases to 2.46 L after it is placed outside on a cold day. What is the
outside temperature in K? in °C?

The outside temperature is 262.1K or -10.9°C

Explanation:

Given that,

Original volume V1 = 2.75 L

Original temperature T1 = 20.0°C

Since unit of temperature is Kelvin, convert 20°C to Kelvin by adding 273 to 20°C

(20.0°C + 273K = 293K)

Outside volume V2 = 2.46 L

Outside temperature T2 = ?

Since volume and temperature are given while pressure is constant, apply the formula for Charle's law

V1/T1 = V2/T2

2.75L/293K = 2.46L/T2

To get the value of T2, cross multiply

2.75L x T2 = 2.46L x 293K

2.75LT2 = 720.78LK

Divide both sides by 2.75L

2.75LT2/ 2.75L = 720.78LK/2.75L

T2 = 262.1K

Hence, the outside temperature in Kelvin is 262.1K. Then, obtain outside temperature in Celsius by subtracting 273 from 262.1K

i.e 262.1K - 273 = -10.9°C

Thus, the outside temperature is 262.1K, or -10.9°C