Elements that are in the same columns (vertical) are chemically similar.
Carbon- Si
Cesium- Na
Krypton- Ar
Magnesium- Ca
Al- try Boron
Br try Cl
These are just the ones I picked but it could be any in the same column
Salad, a bag of different colored pebbles or sand, etc
Its a single Displacement reaction
Weight of the balloon = 2.0 g
Six weights each of mass 30.0 g is added to the balloon.
Total mass of the balloon = 2.0 g + 6*30.0 g = 182 g
Density of salt water = 1.02 g/mL
Calculating the volume from mass and density:

Converting the volume from mL to cubic cm:

Assuming the balloon to be a sphere,
Volume of the sphere =
π

r = 3.49 cm
Radius of the balloon = 3.49 cm
Diameter of the balloon = 2 r = 2*3.49 cm = 6.98cm