Std-10 Most Imp Ch 8 Gseb L-10

In a Std. X class, out of 40 students, 10 students use spectacles, 2 students have positive power and 8 students have negative power and 8 students have negative power of lenses in their spectacles . Generally which type of spectacles do most of the students use ?

What is the pH of 7.0 xx 10^(-8)M acetic acid. What is the concentration of un-ionsed acetic acid. K_(a) of CH_(3)COOH = 1.8 xx 10^(-5) .

Most common bacterial STD is:

The weight of CH_(3)COONa needed to add in 1 litre N/10 CH_(3)COOH to obtain a buffer solution of pH value 4 is ( Given K_(a) = 1.8 xx10^(-5) )