The question asks for the decreasing order of hydride affinity of four carbocations labeled $A, B, C, D$.

However, the actual structures of $A, B, C,$ and $D$ are not present in the provided prompt. Without the carbocation structures, the hydride affinity order cannot be derived from first principles, because hydride affinity depends on the stability/electronic nature of each specific carbocation.

1. What hydride affinity means

For a carbocation,

The more unstable and electron-deficient the carbocation, the greater its tendency to accept a hydride ion, i.e. the higher its hydride affinity.

So, in general:

• Less stable carbocation $\Rightarrow$ higher hydride affinity
• More stable carbocation $\Rightarrow$ lower hydride affinity

Typical stability trend:

with resonance stabilization greatly lowering hydride affinity.

2. Limitation in this question

Since the figures/structures corresponding to $A, B, C,$ and $D$ are missing, a genuine step-by-step comparison of the four carbocations is not possible.

3. Using the stored answer

The stored correct answer is B, which corresponds to:

Thus, based only on the information available, the answer must be taken as:

Decreasing hydride affinity:

4. Final answer

Therefore, the correct option is:

Option B