Is monero, zcash and dash all of them using a private blockchain?
because based on my research monero is using a private blockchain to protect your privacy and make the transaction untraceable that is why monero is so popular i
in the darknet world right?
But zcash is jclaiming the same thing to make transaction with privacy and untraceable also but they are using a public blockchain how can that be possible?
Thanks in advance

Well I think Monero is the best coin out there for anonymity but I don't know about zcash. It doesn't offer that much of anonymity when compared with monero. On the other hand, Dash is good too but it ain't the best coin to use to give yourself anonymity on every transactions. As far as I know most of those cryptos offering anonymity like monero and dash does it the same but only differs in speed and traceability. There are also a lot of coins out there offering the same feature as them although they are new or is still in ICO stage.