Q:

How vunerable is Ubuntu to Ransomware

I'm relatively new to ubuntu.   With all the  news of ransom ware lately I'm curious as to how susceptible Ubuntu is? 

A:

There is always some risk of infections, viruses, being hacked and so on, so care and due diligence is always in order. 
That said, if you only install software using the Ubuntu software manager your risks of problems are quite low.   Slightly higer using apt-get or installing from source but still quite low. 
And when a new Linux attack is discovered, word gets around quickly and patches are not long in coming. 
Plus, hackers and scammers go after large targets, such as Microsoft platforms.   It's rather rare to see Linux exploits flying around.   The do occur, usually after the exploit has been well known and a patch has been created.   The key to safety is to keep your software versions (kernel, services and apps) up-to-date. 
That said, be careful what links you click on, what attachments you open and take care when installing software that checksums match and the package is trusted.