Duplicate content is a complicated subject, it can cause a number of SEO problems. First, if search crawlers visit through too much duplicate content, they may miss some of your unique content. Second, large-scale duplication may dilute your ranking ability. Finally, even if your content does rank, search engines may pick the wrong URL as the "original." Using canonicalization helps you control your duplicate content.
It just means that the mobile version of your website becomes the starting point for what Google includes in their index, and the baseline for how they determine rankings , & answer to your second questions is Yes ,if you will not update your website to the Mobile Friendly version it will bring negative impact on your Website.
Definitely you cannot afford to have broken links on your website If your site has broken links,search engines will view your site as less accessible. That’s why you need to make sure all of your links, both internal and external, are alive and healthy. If Broken you can fix them.
LSI is the process search engines use to find related keywords in addition to your main keywords.
You can answer this like Let me explain you this with one example If Page A has an authority of 80, and Page B has an authority of 20, it’s obvious that Page A will be ranking higher in the SERP. However, if Page A links to Page B, Page A will now pass on some of its authority to Page B. Eventually, you’ll be seeing Page B’s authority and rankings start to rise too! So it can be said that it carries trustworthiness, relevancy, and authority of a site that is transferable through linking one page to another.
The easiest way to find out how many (and which) pages are indexed is by Googling:
site:www.my-domain.com
This will give you a list of all the pages Google currently has indexed.
Domain names are the unique, human-readable Internet addresses of websites.
