To identify the correct symbol used to indicate the pressure at which a chemical reaction is carried out, let's analyze the given options step by step:
1. Option 1: [tex]\(\xrightarrow{250 \, \mathrm{C}}\)[/tex]
This symbol suggests a temperature condition for the reaction, specifically 250 degrees Celsius. It does not convey any information about pressure.
2. Option 2: [tex]\(\xrightarrow{\Delta}\)[/tex]
The delta ([tex]\(\Delta\)[/tex]) symbol indicates that the reaction requires heat or occurs under heating conditions. Like the previous symbol, it does not provide any details about pressure.
3. Option 3: [tex]\(\xrightarrow{2 \, \mathrm{atm}}\)[/tex]
This symbol specifies that the reaction is performed at a pressure of 2 atmospheres (atm). It gives a clear indication of the pressure conditions.
4. Option 4: [tex]\(\xrightarrow{Pt}\)[/tex]
This symbol shows that platinum (Pt) is used as a catalyst in the reaction. It does not imply any pressure information but rather the presence of a specific catalyst.
Based on the analysis above, the symbol that indicates the pressure at which a chemical reaction is carried out is:
[tex]\[
\boxed{\xrightarrow{2 \, \mathrm{atm}}}
\][/tex]
Thus, the correct option is the third one.
