Which of the following acids has the weakest conjugate base?

a....4.2E-09
b...9.2E-03
c....6.3E-06
d....1.2E-01

You wrote only the answers. But to answer the unasked question, here is how you do it.

Kb = Kw/Ka. Kw = 1E-14. Plug in Ka and solve for Kb, then arrange either strong to weak or weak to strong.

To determine which acid has the weakest conjugate base among the given options, we need to compare the values of the acid dissociation constants (Ka) or, equivalently, the values of the pKa (the negative logarithm of Ka). A smaller pKa value indicates a stronger acid.

Since lower pKa values correspond to stronger acids, we can compare the given values of the Ka (or pKa) to identify the acid with the weakest conjugate base.

However, in the options you provided, there are no specific values of Ka or pKa given. Instead, the values given appear to be in scientific notation. To compare them, we need to convert them to regular decimal notation first.

Let's convert the given values to decimal notation:

a) 4.2E-09 = 4.2 x 10^(-9)
b) 9.2E-03 = 9.2 x 10^(-3)
c) 6.3E-06 = 6.3 x 10^(-6)
d) 1.2E-01 = 1.2 x 10^(-1)

Now that we have converted the values, we can compare them to identify the acid with the weakest conjugate base.

Comparing the values:

a) 4.2 x 10^(-9)
b) 9.2 x 10^(-3)
c) 6.3 x 10^(-6)
d) 1.2 x 10^(-1)

From the given options, the acid with the smallest value (weakest acidity) is option a) 4.2 x 10^(-9), which corresponds to 4.2E-09 in scientific notation.

Therefore, the answer is option a) 4.2E-09, which represents the acid with the weakest conjugate base among the given options.