Answer:
2.Increasing the number of bulbs in a series circuit decreases the brightness of the bulbs.
3. When using batteries, increasing the voltage also increases the current in the circuit. An increase in the current is observed when the brightness of the bulb increases.
4. Adding more batteries to a simple circuit will increase the electrical energy, which will make a bulb brighter. (SOURCE: IDOMYTHINK)
5. Placing cells in series increases the voltage in the circuit by 1.5 V for each cell. Increasing the voltage increases the brightness of the bulb.
6. I DON'T KNOW WHAT CONCLUSION IS ASKING ABOUT.