Question

Liquid carbon dioxide is cooled to ______ to obtain dry ice.

• A. $-50°\mathrm{C}$
• B. $-78°\mathrm{C}$
• C. $-87°\mathrm{C}$
• D. $-5°\mathrm{C}$

Answer 1

The correct option is B

$-78°\mathrm{C}$

The explanation for the correct option-

(B) $-78°\mathrm{C}$

• The Carbon dioxide$\left({\mathrm{CO}}_2\right)$ gas is liquefied under pressure to obtain liquid carbon dioxide.
• Liquid carbon dioxide when cooled to $-78°\mathrm{C}$ turns into solid Carbon dioxide also known as dry ice.

The explanation for the incorrect options-

(A) $-50°\mathrm{C}$ - It is not the required temperature to get dry ice.

(C) $-87°\mathrm{C}$ - It is a temperature lower than that required so dry ice will remain solid at this temperature.

(D) $-5°\mathrm{C}$ - At this temperature Carbon dioxide will remain in gaseous form.

Hence, option (B) is correct. Liquid carbon dioxide is cooled to $-78°\mathrm{C}$ to obtain dry ice.