Is it safe to keep your all crypto currency at a single exchange (bitfinnix)?Or one should choose multiple exchanges.
No it is not safe but it is more dangerous than any other anger to your wealth.
If someone will keep all of his coins on one exchange then he will be hostile to his coins. We saw in the past that many excahnges hacked and the hackers got success to escape with our money. Even big exchanges from high securities are hacked in the past. If someone will know about that then he will never keep his coins in one exchange.