m1v1/n1=m2v2/n2

m1=molarity of Na2Co3 =0.2836

v1=volume of Na2Co3 = 20ml

n1=number of moles of HCL =1

m2=molarity of HCL=?

v2=volume of HCL =19.6

n2=number of moles of hcl =2

please calculate this

@ navin 
This is an easy ques , all the value are mentioned in the question the only thing is u have to substitute that correctly , for the term m2 
acc to the question 
m1v1/n1= m2v2/n2 
so, by calculating 
m1v1n2 = m2v2n1 
or m2v2n1 = m1v1n2
so, by  arrenging the equation 
m2 = m1v1n2 / v2n1 
now substitute the value and get the answer 
here the answer will be 0.57 
HOPE IT CLEARS YOUR DOUBT 

It is wrong, how the no. of moles of Na2CO3 could be 1?, please use the values as per the balance chemical equation.