How many true-breeding pea plant varieties did Mendel select as pairs, which were similar except in one character with contrasting traits?

The number of contrasting characters studied by Mendel for his experiments was:

Which one from those given below is the period for Mendel's hybridization experiments?

How many pairs of contrasting characters in pea plants were studied by Mendel in his experiments?

According to Mendelism which character is showing dominance:

1. Terminal position of the flower

2. Green colour in the seed coat

3. Wrinkled seed

4. Green pod colour