A balanced Wheatstone bridge $\text{ABCD}$ has the following arm resistances: $R_{AB} = 1\:k\Omega \: \pm \:2.1\%; \:R_{BC} = 100\:\Omega \:\pm \:0.5\%; \: R_{CD}$ is an unknown resistance; $R_{DA} = 300 \:\Omega \: \pm \:0.4\%$. The value of $R_{CD}$ and its accuracy is

1. $30\:\Omega \:\pm \:3\:\Omega$
2. $30\:\Omega \:\pm \:0.9\:\Omega$
3. $3000\:\Omega \:\pm \:90\:\Omega$
4. $3000\:\Omega \:\pm \:3\:\Omega$