Dear student
Alkenes are more susceptible for electrophilic addition reaction in which electrophile attacks on the π orbital of double bond followed by the attack of negative part.
According to the proposed concept of markownikoff addition of electrophile, negative part must go to the carbon having lesser number of hydrogen.
So, the addition of HCl to will give 2-chloropropane.
So, X is 2-chloropropane
Regards.