The first man made fibre is

Rayon

Explanation:

Rayon developed for the first time in the late 19th century as a replacement for silk. Silk was expensive in those days as was an organic product made out of cocoons. Rayon was the first man-made fibre came to be known as an artificial textile material formed from cellulose obtained from plants. Rayon was a less expensive option for silk clothing and accessories.

the answer for sodium is 0.186

the answer for rubidium is 0.251

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2