an astronaut is said to be weightless when he/she travells in a satellite . does it mean that the earthdoes not attract him/her ?

As long as they’re in a range where earth’s gravitational force can act on them. They cannot be considered weightless.

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current