Question

When a List resizes because there is no more excess capacity, how much capacity is added? just 1? Or does it add Capacity (so doubling the total capacity)?

Answer 1

The capacity will double.

This is controlled by the following source:

// Ensures that the capacity of this list is at least the given minimum
// value. If the currect capacity of the list is less than min, the
// capacity is increased to twice the current capacity or to min, 
// whichever is larger.
private void EnsureCapacity(int min) { 
    if (_items.Length < min) { 
        int newCapacity = _items.Length == 0? _defaultCapacity : _items.Length * 2;
        if (newCapacity < min) newCapacity = min; 
        Capacity = newCapacity;
    }
}

_defaultCapacity is a const int equal to 4.