Are condoms always effective? what are the chances of them breaking ?

Not always effective: Male condoms are somewhere around 82-98% effective. I don't know the exact risk of breakage, but if a lubricant is used, it should be water based like KY jelly. Oil-based lubricants like petroleum jelly, massage oils or lotions can increase the risk of breakage.

No: Always & never are seldom true with anything. Condoms can fail just like any other form of BC other than abstinence. Men may buy condoms too big, or not apply them before any sexual activity, which both increase failure rate. They don't protect against all STD's either. Proper use gets failure rate down below 10%, but breaking is rarely the problem if you respect the "use by" date on the condom,