Which solution would most likely cause a plant placed in it to become more firmer and rigid

When a plant cell is placed in a hypotonic solution, it becomes firmer and more rigid. A hypotonic solution is the one, which contains less concentration of solute and more concentration of solvent ( water) outside the cell as compared to inside.

Explanation:

there you go :)A hypotonic solution is the one!

weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

here's your answer.