The 10 .NET Concepts Every Interviewer Checks

Across hundreds of .NET interviews the same concepts come up because each one branches into a useful conversation. Know these ten and the thread each one opens.

1. Value vs reference types → boxing → why generics exist.
2. IEnumerable vs IQueryable → deferred execution → where the filter runs (memory vs database).
3. async/await → “does it create a thread?” (no, for I/O) → why it helps server throughput.
4. Dependency Injection → loose coupling → IoC → service lifetimes.
5. Service lifetimes → Transient vs Scoped vs Singleton → why DbContext is scoped → captive dependency.
6. The ASP.NET Core pipeline → middleware ordering → “where does authentication go?”
7. Indexes → clustered vs non-clustered → key lookup → covering index.
8. Execution plans → seek vs scan → estimated vs actual rows → stale statistics.
9. EF change tracking → AsNoTracking → N+1 → projection into a DTO.
10. A scenario question → your method for reasoning under uncertainty.

Each of these has a full answer, a spoken version and its follow-up chain on Prismita. Work through one thread a day.