Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.

 

Let me try to answer your questions in their respective order:

 

1- If your exam or experiment interferes with your prayers, you ought to ask: Do you have the option of doing it in such a way that it does not conflict with your prayer times? If you have, then you should not combine. If however, you have no such option, then you are allowed to combine Zhuhr with `Asr either at the time of the former or the latter; likewise, you may combine Maghrib and `Ishaa’.

 

2- If you happened to make this mistake in the past while you had a choice not to do it, then you ought to ask forgiveness. You should resolve never to do it again. If you can combine Zhuhr with `Asr before the expiry of the time of the latter, you may do so in such circumstances. We learn from Ibn `Abbas that the Prophet (peace be upon him) combined prayers to set a precedent for his community that they are allowed to do so when faced with hardship.

 

4- If you can go to the mosque to pray Maghrib, you should so; if you find it hard then, you are allowed to combine. You should make this judgment for yourself based on your moral conscience. The Prophet (peace be upon him) “Consult your conscience – even if they give you a ruling.”

 

4-    In such cases you are allowed to combine prayers as long as they did not set aside prayer times and places.

 

Almighty Allah knows best.