congruent circles
No. Concentric circles have the same centre but not [usually] the same radius. Congruent circles have the same radius, but not [usually] the same centre. If you have two concentric congruent circles one will be exactly on top of the other.
They are said to be concentric circles.
mandorla or vesica piscis (if they have the same radius)
You need some more information about any of the circles, or about the relationship between the two circles, to answer this question.
Two figures are congruent if you can "pick one up" and then place it down on top of the other one in such a way that the two exactly overlay each other... in other words, if they are the exact same shape and size. So, any two circles will always have the same shape, but not necessarily the same size. Only circles that have the exact same size (as measured by matching radius, diameter, circumference, or surface area) are congruent.
The same radius.
No. Concentric circles have the same centre but not [usually] the same radius. Congruent circles have the same radius, but not [usually] the same centre. If you have two concentric congruent circles one will be exactly on top of the other.
They are said to be concentric circles.
If you create third circle with radius 2, then all the points on that circle would be equidistant form both circles. So the answer is a circle with radius 2.
mandorla or vesica piscis (if they have the same radius)
If the circles have the same radius then an infinite number, and if they do not, then none.
Multiply the radius by 2.
Concentric circles are the circles with the same center therefore they do not cross with each other as the "center is not considered a point on the circle". An exception would be two circles that are concentric and have the same radius, in which case the circles are indistinct and every point of the circles is an intersection.
Two circles that don't have the same center point are called "non-concentric circles." These circles can have different radii and may or may not intersect each other. If they intersect, they will do so at two points, one point, or not at all, depending on their sizes and positions.
You need some more information about any of the circles, or about the relationship between the two circles, to answer this question.
Two arcs are congruent if they have the same measure in degrees or radians and are parts of the same circle or circles of equal radius. Additionally, if the arcs are on different circles, they must subtend the same central angle. This ensures that the lengths of the arcs are equal, meeting the congruence condition.
Two figures are congruent if you can "pick one up" and then place it down on top of the other one in such a way that the two exactly overlay each other... in other words, if they are the exact same shape and size. So, any two circles will always have the same shape, but not necessarily the same size. Only circles that have the exact same size (as measured by matching radius, diameter, circumference, or surface area) are congruent.