Q1. Why it is considered Fardh-e-Kifaya to know the date based on Hijri Calendar?
Q2. Is there any virtue of killing Lizard, etc?
There are many Laws in Shariah that are based on the lunar calendar. Fasting in Ramadaan, Haj, Zakaat, etc. are some of the laws that are based on lunar calculation. If one does not keep track of the lunar calendar, then it will not be possible to carry out these laws of Shariah in its correct and appropriate time.
There are Ahadith wherein Rasulullah (salallaahu Alayhi Wasalam) has mentioned to kill the lizard. This was due to lizard assisting in igniting the fire that was intended to destroy Ebrahim Alayhis Salaam. The quicker a person kills a lizard the greater the reward.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai