how to know 10 rupees coin is fake
This coin is rumored to be a fake one due to chaos on social media. However, the Reserve Bank of India (RBI) issued an official statement to address these rumors declaring that the old the design prior to 2011 is valid and is legal tender. 
The third design of the ₹10 coin, minted since 2011 features the lettering “भारत” on left and “INDIA” on right on the outer ring, and the year of mint and mint mark below. At the center part of the coin’s obverse is the Lion capital with the lettering “सत्यमेव जयते” below it. On the reverse it features 10 notches with the ₹ sign below it, and the number 10 below the ₹ sign.  
2. While explaining the reason for minting a different set of coins, the Reserve Bank of India (RBI) said that since currency coins have longer life, the coins of different designs and shapes circulate in the market at the same time.
9. The oldest Rs. 10 coin was issued on March 26, 2009. The face of the coin is divided into three portions with two horizontal lines. The centre portion bears the lion capitol of Ashoka pillar with “satyamev jayte” written in Hindi written below.
Rumors on fake 10 Rupee coins, started a few months ago. It is popularly believed that shopkeepers and some traders may have spread malicious rumors, that many 10 rupee coins were fake. A message was also circulated on WhatsApp, on how to find the difference between a fake and real 10 rupee coin. This was believed to be the handiwork of a neighboring country.
The RBI has asked you not to listen to any rumors on fake 10 rupee coins. The 10 rupee coins are still valid. These were some of the popular rumors on how to distinguish between fake and real 10 rupee coins. These rumors were found to be false.
The Reserve Bank has advised members of the public not to give credence to such ill-informed notions and ignore them and continue to accept these coins as legal tender in all their transactions without any hesitation.”
Note-As I expected, RBI came up and clarified the news of fake Rs.10 coin as RUMOR. The RBI released a press statement on 20th Nov, 2016 in this regard stating “The Reserve Bank of India puts into circulation coins minted by the Government of India. These coins have distinctive features. Coins in new denominations to meet transaction needs of public and coins in new designs to reflect various themes – economic, social and cultural – are introduced from time to time. As coins remain in circulation for longer periods, it is quite possible that coins of different designs and even shapes are circulating at the same time. One such change is introduction of ‘Rupee symbol’ in coins in July 2011. An instance of this is the Rs.10 coins with rupee symbol and the same denomination coin without rupee symbol. Both of them are legal tender and equally good for transactions, though they may look a little different.
A senior RBI official said no money that is judged to be a fake can be exchanged for real currency. “Fake currency, whether it is a coin or a note, is not a legal tender,” he said, meaning these are not recognised by the RBI.
Zahidul Islam, who runs a computer sales and service shop in Ratua, today came to Malda town that is almost 35km
from his home for just one thing — he wanted a bank to take his 150 coins of Rs 10 denomination and check if there were any fakes. The nationalised bank declined to check, saying it did not have the expertise.