Better method for preparation of BeF₂, among the following is :

Solution

Chemistry ma’am · 3 steps

Skip the fluorine gas: heat a salt that already holds the fluorides, and BeF₂ is left behind.

1. Why it is tricky. BeF₂ is needed anhydrous, so it cannot be crystallised from water. Beryllium salts hold on to water strongly, and heating the hydrate tends to hydrolyse it instead of drying it.
2. Standard method. Heat ammonium fluoroberyllate, (NH₄)₂BeF₄. It breaks up cleanly, the ammonium fluoride part leaves as vapour, and pure anhydrous BeF₂ stays behind.

   (NH₄)₂BeF₄ →(Δ) BeF₂ + 2NH₄F

   Route	Problem
   BeH₂ + F₂	BeH₂ is itself hard to make, and F₂ reacts violently
   (NH₄)₂BeF₄ on heating	none: easy to handle, volatile by-product, pure anhydrous BeF₂
   Be + F₂	Be has a protective oxide film, and F₂ is hazardous and costly
   BeO + C + F₂	this is the BeCl₂ method with Cl₂, not a good fluoride route

3. So. The better method is the thermal decomposition of (NH₄)₂BeF₄, option (b).

The idea to keep. Anhydrous BeF₂ comes from heating (NH₄)₂BeF₄. Anhydrous BeCl₂ comes from BeO + C + Cl₂ at 600 to 800 K. Keep the two routes paired in your head.

Answer from the NTA final answer key. Solution by PrepWiser.