Please help with this... 4. What is the pH of a 4.7 x 10-9 M HCl solution?

a. 4.67
b.- 8.33
c. 11.21
d. 2.93​

Idon’t know how to solve this question

7. what temperature is need to just dissolve 50 g of nh4cl in 75 g of water? '

The alkali metals (group 1) consist of lithium (3), sodium (11), potassium (19), rubidium (37), cesium (55), and francium (87). they are soft, metallic solids with low densities and low melting points. based on the data shown in figure 1, how many valence electrons do alkali metals share?