It means that you consider the elements as a list organized by atomic number, the property is seen to repeat over and over as you move through that list.
Answer: 
Explanation:
Given
Current in the first wire 
Current in the second wire 
wires are
apart
Force per unit length between the current-carrying wires is

Force exerted by the wires is the same
Put the values

This force will be repulsive in nature as the current is flowing opposite
Not necessarily, object A could also be neutral, and becoming a dipole due to object B's charge. A charged object can induce a dipole in a neutral object, and that object would then become attracted without being charged.
Answer:
Oh I had this question before! :)
Explanation:
Acid - citrus products - the classic one is lemon juice
Anything with a sour taste is acidic
Base - soap, oven cleaner, drain cleaner, baking soda
Basic things are bitter (please don't taste the drain cleaner and oven cleaner)
A. A fast moving stream. Water has erode Earth for thousands of years. This was what caused the Grand Canyon. A faster ,owing stream would cause a faster erosion due to the speed and strength of the water itself.