(Solved): Peter wants to test the effects of road salt on the plants that grow along the side of the highway. ...

Peter wants to test the effects of road salt on the plants that grow along the side of the highway. He chooses a species of crab grass for his experiment. After allowing 100 crab grass seeds to germinate in pure water he then transfers the seedlings into soil. He plants 10 seedlings into 10 different containers. Containers \( \# 1 \) and \( \# 2 \) are watered with pure water ( so \( 0 \% \mathrm{NaCL} \) ). Containers #3 and \( \# 4 \) are watered with a solution of \( 2 \% \mathrm{NaCl} \). Pots \( \# 5 \) and \( \# 6 \) are watered with \( 4 \% \mathrm{NaCl} \). Pots \( \# 7 \) and \( \# 8 \) are watered with \( 6 \% \) of \( \mathrm{NaCl} \). Finally containers #9 and \( \# 10 \) are watered with \( 8 \% \mathrm{NaCl} \). After 6 weeks Peter measures the growth in each container by removing the plants from the soil and weighing the mass of plant material harvested from each container. What is the independent variable in Peter's experiment? the number of crab grass seeds he planted in each pot the concentration of salt in the solutions he used to water the plants. the mass of the plants after 6 weeks of growth the amount of salt solution he used each time he watered the plants